Obviously he's not only selling Iranian names.
That's what he did. Telling users it is their own fault that he had to take their names and sell them. You were causing issues, because you did not log in for three months.
Durov has been funding it with his own savings for more than 8 years, which is great but a project as big as Telegram eventually needs more funding, especially when it's literally Messenger + Google Drive + Social Media + Privacy Respecting. It's hard to make money when the world runs on selling data and obviously, Telegram Premium has not been very successful.
I do not mind the auction of the usernames to be very honest as I understand why they're being auctioned in the first place.
Arbitrary or not, I'm a Telegram super-user, out of the 20 public groups and channels that I have, only one had its username take away and only because it was inactive. Could be a glitch, could be intentional but I do know that it's partly because of me that the channel looked like a dead one.