@guenther the original author did not claim a violation, they wrote that it "raises questions about the legality of this situation". The question being, in my interpretation, if the code has a centralized copyright or not. I have said in the past that AGPL alone is not enough to protect a project from suddenly changing direction.
Linux resisted acquisition from both Google and Microsoft for decades because of the combination of copyleft and its distributed authorship, which makes it impossible to buy it straight off Torvald's hands.
Everyone has a price, #signal was already very openly sponsored by google, helped whitewashing facebook and had to push people to google market by boycotting all other distribution channels, and demonize decentralization in return.