You could say this was just meant as a cute, harmless compliment. But even if you don’t call this “harassing,” it is, at very best, a deeply cheesy way to make your admiration of someone known. Why not just say, “You’re awesome on the show! Big fan!”
(It could also have been a deliberate joke, riffing on the very harassment controversies that FtB and others have recently been embroiled in. But if so, jokes like that tend to work only when both parties involved know one another personally, know each other’s boundaries and sense of humor, and know such jokes are okay within those boundaries. Kind of not a joke you’d pull on an stranger and expect them to get it.)
Addendum: Since there’s a certain contingent of people in the comments (naturally) invested in making the case that John is simply being sweet and asking a perfectly innocent question, and anyone who thinks otherwise is just overreacting with a broom handle wedged where broom handles don’t go — well, there’s been a brief follow-up exchange with Jen where he shows his hand: he’s trolling.