Maybe he found out you were ripping off his work and deleted his account.
But the usual suspects are the indie community bullying and calling his work A.I slop(real or unfounded), him being caught out on using A.I while he said "I did not use any A.I assets or code"
Or him actually just being an asset flipper that will just delete his account and submit the game as new to a gamejam to win prizes. Yes, I have seen this happen.
He will be baaarrrrck!