The community probably would have complained if they registered the trademark preemptively. But if they let the bad guys register it and then save the day it's the least bad solution.
The timeline just seems like two different brands wanted the name. atSign was using atProtocol as their thing. And trademarks are defend-or-lose. That AT Proto would grow so much more than atSign is just a thing we know now. They were both contemporaneous and it doesn't seem to have been some kind of gazumping operation so much as two groups landing on a name.