That's what I suspect, and not just an AI band, but an AI festival with an entire bill of AI bands.

But I still haven't found anything to verify that - there's little hints scattered through the comments, like references to "creators" and such, and a notable lack of coverage anywhere else. And, the more I've paid attention, a suspicious sameness to the audience. And there's a band elsewhere on the bill - on one of the festival compilations - that looks like five vtubers just pulled straight out of their streams and rendered with instruments.

It's disappointing. I still think the song is excellent, but my enthusiasm for it sort of dried up and blew away somewhere along the way.

It's not the artificiality - I've been listening to and watching vocaloids since the Miku Black Rock Shooter days, so virtual musicians don't bother me. It's the apparent deliberate attempt to hide what they are.

And actually, thinking about it, I could see a Teto version of that song...