from my admittedly brief research into it, $GAS was sending him transaction fees, as it desired the association. So it wasn't him selling a tangible number of coins to a particular person. So I figure to pay it back, he'd have to trace down the owners of every tx and pay them back the tx fee. Perhaps that's easy, perhaps its non-trivial. According to the tweet[0] he made yesterday, in order to donate the combined funds to charity he has to submit 230 separate transactions on his phone.

[0] https://x.com/Steve_Yegge/status/2044114434348724351