"It's like some kind of cosmic convergence."
The three acts, he pointed out, released their breakthrough albums within months of each other in 1994. And now here they were, more than two decades later, headlining this annual year-end blow-out presented by Los Angeles' influential modern-rock radio station.
What Beck didn't say — but what the show made clear — is that lately he and his fellow veterans have been getting in the spirit of those early days following separate periods of experimentation.
So maybe the cosmic convergence was merely an alignment of earthly strategies, including those of KROQ itself, which benefits from any reminder of the era before digital streaming began threatening radio's importance.
For Green Day — introduced Sunday by two other '90s survivors in No Doubt's Adrian Young and Tony Kanal — looking back means paring down: "Revolution Radio," the Bay Area trio's latest record, is its first since 2000 not to carry an overarching concept, be it the rock-operatic storytelling of 2004's "American Idiot" (which later became a successful Broadway musical) or the triple-album sprawl of "¡Uno!," "¡Dos!" and "¡Tré!" in 2012.
“This is my high school band, baby!” frontman
But if Green Day was returning to its old sound for new songs such as "Bang Bang" and "Revolution Radio," Armstrong wasn't ignoring current events.
In the former he narrated the disturbed thoughts of a mass shooter, and he linked the latter to what he called the "chaos" of 2016, which for him includes the spread of fake news and the recent deadly warehouse fire near the band's hometown.
He also triggered a cascade of boos in the audience by invoking Donald Trump's name before "Know Your Enemy."
Weezer stayed away from such political grandstanding — no surprise, given the L.A. band's almost exclusive commitment to songs about being misunderstood by women.
But like Green Day, Weezer was channeling the pop-punk approach of its early work, both in hits from the group's self-titled debut (including "Say It Ain't So" and "Buddy Holly") and in fresh material from another self-titled album that came out this year ("King of the World," "Thank God for Girls").
Gone were the forays into hip-hop and death metal with which frontman Rivers Cuomo amused himself — and few of the band's fans — several years ago.
Yet the performance didn't feel like a retreat. Though Weezer's new songs take up a crowd-pleasing mode, Cuomo's lyrics are more personal and idiosyncratic than ever. "Thank God for Girls" oozed messy emotion even as the guitars chugged in neat post-grunge formation.
For Beck, messiness is the crowd-pleasing mode. Boisterous cheers greeted him when he came onstage to the sound of "Loser," the shaggy 1994 hit that made him an instant left-field celebrity. And the enthusiastic response continued for "Devils Haircut" and "Where It's At," key tracks from his magpie's masterpiece, "Odelay."
More recently, Beck has cleaned up his act, as on 2014's "Morning Phase." A carefully produced set of dreamy folk tunes, the record earned warm reviews and even won a Grammy Award for album of the year.
But it also gave Beck the air of a genteel old-timer, one who inspired only mild applause at the Forum with the album's drowsy (and very beautiful) "Blue Moon."
Perhaps this is why the singer has re-embraced his signature cut-and-paste vibe for "Dreams" and "Wow," two singles from the "Morning Phase" follow-up he's said to be close to finishing.
On Sunday, he played the trippy, densely textured songs back to back after "Blue Moon," and the message seemed as clear as Green Day's opinion of the president-elect: Beck is making alt-rock weird again.