If you know a teenager, chances are the kid listens to more than one radio station regularly. Chances are the kid likes more than one genre of music. Chances are the kid knows someone who went to see Twenty One Pilots on Friday night at the sold-out Xcel Energy Center in St. Paul.

Twenty One Pilots is not the kind of band a talent scout for a major record label would instantly fall in love with. What genre are they? What radio format do they fit in? How do you market them?

Twenty One Pilots — actually just two 20-something dudes from Columbus, Ohio — are the kitchen sink of popular music. They mix emo and angsty lyrics, Macklemore-like raps, Fall Out Boy-ish energy, Charlie Puth-ian piano pop, 311-styled reggae rhythms, EDM beats, Blue Man Group anonymity and even a little Eddie Vedder-esque ukulele strumming into an intoxicating, hard-to-classify concoction that the teens and 20-somethings can’t get enough of.

That the X was packed with 15,000 fans was not surprising, even though TOP played at the 3,300-capacity Myth nightclub in Maplewood just last fall. The fans sang along with nearly every song, especially those from the No. 1 album “Blurryface.” That the fans were nonplused about the myth and illusion of TOP wasn’t a surprise either.

Millennials are so accustomed to singing stars lip-syncing in concert that the fans on Friday probably didn’t care that most of the music they heard was recorded and not performed live by drummer/trumpeter Josh Dun and keyboardist/bassist/ukulele player/singer Tyler Joseph.

The fans probably didn’t care if that was really Joseph, wearing TOP’s familiar uniform of knit ski mask, red blazer, skinny black pants and necktie, singing “Hometown” onstage, where he was quickly covered with a giant tarp by roadies and — presto — magically appeared a few seconds later singing amid fans in Section 103 without his mask.

Dun and Joseph later donned different masks, those of skeletons, for a mini-set on a stage in the middle of the arena. There, Joseph proved he really can sing, packing plenty of emotion into the epic “Ode to Sleep.”

And he clearly was playing his uke on “Lane Boy,” TOP’s ode to finding their own path in music. It mashed up sweet-sounding ukulele with dance hall reggae raps as Joseph declared, “If it was our way, we’d have a tempo change every other time change.” It was TOP’s way of saying, “Industry experts be damned.”

Quibble all you want about too much genre-blending and how much of the music was live because, ultimately, TOP entertained their audience. Joseph, 27, and Dun, 28, supplied the energy, the emotion and the flash — dazzling lights, striking video images, stage fog blasters, confetti showers and Dun tumbling inside a “hamster ball” à la those Gen X favorites Flaming Lips.

TOP didn’t really need backup singers because the fans sang robustly, especially on the hits, the reggae-flavored “Ride” and the anthemic “Stressed Out,” and the closing power ballad “Trees.” But members of the two opening acts, ChefSpecial and Mutemath, joined Twenty One Pilots for a medley of covers — the Isley Brothers’ “Twist and Shout,” Celine Dion’s “My Heart Will Go On” (complete with these alt-rock dudes dancing in unison steps), Justin Bieber’s “Love Yourself” and House of Pain’s hip-hop classic “Jump Around.”

This hodgepodge of songs of different styles from different eras — which, once again, had fans singing along — proved that, contrary to what the industry pros think, a kitchen sink approach to popular music can truly work.