He sounded only a little more convinced in the locker room several hours later after his side continued its recent scoring spree in a 5-0 victory over the Portland Timbers in front of 21,207 fans at StubHub Center.
The Galaxy has scored 16 goals in its last three competitive matches, two of those Major League Soccer contests.
"We played very well at times," Arena said. "After about the first 10 or 12 minutes we settled in and played our game."
Playing its second of four home contests in a five-game stretch, the Galaxy wasted little time taking command against the Timbers.
In the 13th minute, midfielder Sebastian Lletget found the lower left corner from 15 yards out.
Five minutes later, captain Robbie Keane converted a penalty kick after Lletget was taken down in the penalty area by Maximiliano Urruti.
"Sebastian was our best player in the first few minutes, he created several chances and it was good to see him get the first goal," Arena said.
In the 33rd minute, defender Robbie Rogers scored his first goal in a Galaxy uniform, redirecting a through ball from Keane to make it 3-0.
His last MLS goal was in 2011 with Columbus.
"That was his first goal?" Arena asked. "He should have about 10. He makes things happen out there."
Juninho increased the lead to 4-0 in the 72nd minute for the Galaxy (7-5-7), which moved into sole possession of third place in the Western Conference, one point behind Seattle and Vancouver.
It was the Brazilian midfielder's third goal of the year and second in two games.
The Galaxy struck again in the 88th minute when Jose Villarreal sneaked a direct free kick inside the left post.
Portland (7-6-4) had its franchise-record four-game league winning streak broken and dropped to fourth, one point ahead of idle Sporting KC.
The Galaxy has 10 goals from 10 different players in its last two games.
"All by design," Arena said. "That's the way we drew it up. Actually, I wouldn't mind if one guy scored five goals either, but this shows everyone's involved and we're moving the ball better."
The teams played to a 2-2 draw in Portland on March 15, when Alan Gordon scored the equalizer in stoppage time for the Galaxy, which remains undefeated against Portland (6-0-1) at StubHub Center.
Gordon replaced Lletget in the 66th minute Wednesday.
English midfielder Steven Gerrard, who signed with the Galaxy in January, is scheduled to join the roster in July following Liverpool's season in the Premier League.
In 17 seasons with Liverpool, the 34-year-old captain scored 182 goals in 696 games.