It appears to have been genuine. He's not much of an actor.
I’m aware of the existence of “That 70s Show,” but I lived through the 70s and wouldn’t consider watching a TV show about it. Ne zot! I divide young actors into “the ones with blond hair” and “the ones with brown hair.” Kutcher has brown hair, iirc.
I almost had to be resuscitated during a recent episode of Big Bang Theory” (Season 2, Disc 1), though. Tom kicked me a few times as I was gasping on the living room floor.
Don't overestimate him. He had a script to work from on the show.