Thinking and knowing are different things in Week 1 of NFL season

As usual, the first weekend of the NFL season was an exercise in what we didn’t know.

We thought: San Francisco’s Colin Kaepernick would be hurting for receivers. We learned: Kaepernick, who had never thrown for 300 yards, finished with 412 yards and three touchdowns in a 34-28 victory over Green Bay. Anquan Boldin caught 13 passes for 208 yards, and tight end Vernon Davis had six catches for 98 yards. In all, Kaepernick completed 27 passes to seven players.

We thought: Buffalo’s EJ Manuel, Oakland’s Terrelle Pryor and the New York Jets’ Geno Smith probably would look like bottom-of-the-barrel starting quarterbacks. We learned: Manuel and Pryor nearly led their teams to upsets of New England and Indianapolis, respectively, and Smith worked some last-minute magic in an 18-17 victory over Tampa Bay. The Jets rookie was aided by a boneheaded late hit by Buccaneers linebacker Lavonte David.

We thought: It was just a hiccup that Pittsburgh missed the playoffs last season. We learned: The Steelers have a long way to go. They lost at home to Tennessee, 16-9, and didn’t score their first offensive points until 1 minute 26 seconds remained. Along the way, they lost Pro Bowl center Maurkice Pouncey (torn knee ligaments) and linebacker Larry Foote (ruptured biceps) to season-ending injuries.

We thought: Former New Orleans defensive coordinator Gregg Williams was pretty much done in the NFL after Bountygate. We learned: In his new role as a defensive assistant coach in Tennessee, Williams already is making an impact. The Titans gave up more points than anyone last season, but Sunday were smothering against the Steelers.

We thought: Miami couldn’t win an opener, having lost six of its previous seven. We learned: The Dolphins can win, although it helps to be playing Cleveland, which is 1-14 in openers since the franchise re-formed in 1999.

We thought: New England couldn’t replace Wes Welker, slot receiver extraordinaire. We learned: Danny Amendola isn’t a shabby alternative. He had 10 catches for 104 yards and was clutch in the middle of the field when Tom Brady needed him most.

We thought: With a great start, Buffalo had reversed its fortunes against the Patriots. We learned: The Bills couldn’t quite get there, dropping to 1-19 in their last 20 against New England.

We thought: Crucial errors were the calling card of replacement officials. We learned: Regular officials can make them too. In the Green Bay-San Francisco game, the 49ers were mistakenly awarded an extra third down and scored a touchdown on it. Upon further review, after offsetting penalties, the down should have been fourth.

We thought: We can’t expect much from two-win teams. We learned: That doesn’t apply to the Kansas City Chiefs, who pounded Jacksonville, 28-2. It was an impressive debut for new Coach Andy Reid, quarterback Alex Smith and a Chiefs defense that allowed the Jaguars past their own 36 once.

We thought: Seattle was a Super Bowl contender. We learned: It won’t be an easy road to get there. Carolina gave the Seahawks all they could handle in a 12-7 Seattle victory. It was the first time in four years that Coach Pete Carroll won a road opener.

We thought: Andrew Luck beats you with his arm. We learned: The Indianapolis quarterback has some serious wheels, carving through Oakland’s defense for a 19-yard touchdown with 5:20 left, the clinching score in a 21-17 victory. It was Luck’s eighth game-winning drive in 17 starts.

We thought: It’s unusual to score a safety. We learned: It wasn’t out of the ordinary Sunday. Before the season was one quarter old, the Jets, Steelers and Jaguars picked up two points each.

We thought: New Orleans had a long way to go with its defense, historically bad last season. We learned: The Saints looked occasionally shaky but ultimately good enough in a 23-17 victory over the high-octane Atlanta Falcons. That included sacking Matt Ryan three times, forcing two pivotal turnovers and limiting Atlanta to a three-for-11 conversion rate on third down.

We thought: Lions defensive tackle Ndamukong Suh had learned his lesson about playing dirty. We learned: That was wishful thinking. Suh dived at the knees of a Vikings lineman on an interception return, wiping out a Detroit touchdown and perhaps earning himself an XXL-sized fine.

We thought: Adrian Peterson would be hard-pressed to repeat as a 2,000-yard rusher, something no one has done. We learned: The Minnesota Vikings star and defending NFL most valuable player ran for a 78-yard touchdown the first time he touched the ball against Detroit.

And then?

Peterson gained 15 yards in his next 17 carries.

Fan falls to death

A fan fell to his death at Candlestick Park during the Packers-49ers game, and two more were injured in a fall at the end of the Raiders-Colts game.

In San Francisco, a man who appeared to be in his 30s and reportedly looked intoxicated fell from an elevated pedestrian walkway. According to the Associated Press, he fell just after kickoff, and off-duty medics and police officers gave him first aid until an ambulance arrived, but the man was pronounced dead from his injuries.

Two fans were injured at the end of the Colts game when a railing gave way and they fell onto the Raiders’ field tunnel. They reportedly received immediate medical attention at the scene.

According to WISH-TV, one of the fans was checked out at the stadium and released, and the other was transported to IU Health Methodist Hospital as a precaution for evaluation.

Citing medical officials, WISH said the injuries did not appear to be serious.

Paying penalties

Two NFL linebackers, former teammates at USC, made some questionable decisions Sunday.

Green Bay’s Clay Matthews made a leaping, clothesline-type tackle of Kaepernick after the quarterback had stepped out of bounds. That triggered a brawl. Although Matthews was flagged, so was 49ers tackle Joe Staley, who rushed over to defend his quarterback. Matthews and Staley got offsetting penalties.

In Chicago, Cincinnati linebacker Rey Maualuga was flagged for unsportsmanlike conduct with 1:06 remaining in a one-score game.

The Bengals had just stopped the Bears on third down and probably would have forced a punt. But Maualuga got in a pushing match with an offensive player, was penalized, and handed the Bears a first down and the ability to run out the clock.

“Unfortunately,” Bengals Coach Marvin Lewis said, “we had a lot of guys lose composure today.”

sam.farmer@latimes.com

Twitter: LATimesfarmer