That's totally separate from the algorithm/genre issue though. The genres have never ever really perfectly matched up with the music but it doesn't matter. If the algorithm perfectly selected more music you like you still wouldn't be more likely to look up the name of the track I don't think.
Anyway that soundtrack is... not jpop per se but it is heavily influenced by it. The format and aesthetics are very jazz-like but the rhythms and harmonizations are very jpop. That might not be the most _useful_ association in this context of finding music that sounds similar, but it is there. And in its way as accurate as calling it jazz. Saying it's "actually" jazz or funk is... that's just not really how this works. It's not wrong to say it's jazz but it's wrong to say anything really is ONLY jazz, and can't also be other things too.