This definitely sounds like a Drifting Away cover! I'm really glad to hear it here as this my favorite WarioWare lyrical song by far (Tommorow Hill is the inly one that may be close to it)
Though I doubt this means we'll get more WarioWare stuff than usual in MKWorld. Perhaps it's like Smash Bros where they let you pick the song you want for the track and have several remixes of past Mario music.
Just about every song is random in this game. Virtually every previous Mario Kart track theme returns as part of the soundtrack, even if 99% of those tracks don't return.The odd thing about it is that the course doesn't otherwise appear to be based on anything that one might associate with Drifting Away, which may lend credence to it just being a random song selected in lieu of whatever music normally plays there as suggested in #2. But who knows, maybe there'll be a proper WarioWare stage and/or characters.