So they generated all of them, as MIDI sequences, and stored them on a hard drive.[1][2] Arguably, all those are now public domain

Not really though. If this were accepted as a creative work, then it also violates the copyright of every modern song. But, as exemplified the the story in the OP, where the author gets the idea from is really important. So, you could look a jury in the eye and say you were just browsing through a hard drive full of melodies and picked one that seemed good, but that likely isn't going to fly.