Sure, but that seems to be belied on its face by them having actually stripped the present-by-default mentions & links:
> neither the terms nor any other part of the website contained any references to Mastodon, nor any links to the source code, which are present in Mastodon’s user interface by default.
That, then, would be extremely strong evidence that they're lying, and I would expect more than enough for a legal injunction.
You have to be able to say, with a straight face, that you really believe that they did the thing you’re accusing them of.
So just because it’s theoretically possible that there’s a path to the facts we see without violating the license, the fact that a license violation is a plausible explanation is enough to launch a court case.
After all, the court case including the discovery process and the trial itself are all about determining the relevant facts.
That’s not really how courts work. You don’t how to have all the evidence to support your claims when you file the lawsuit.
Rather, you can go to court saying “I have reason to believe Doe is doing thing X, it’s causing me harms Y, and we could prove it with Z”.
If the case is not dismissed at an early stage, then the discovery process is started. This gives subpoena power to both sides to discover relevant facts about the case, hold depositions under oath with relevant parties, and other means of gathering information that wouldn’t be available outside of the court process.
It’s very likely that the Truth Social source code would have to be turned over to the plaintiffs during the discovery process. Additionally, the plaintiffs lawyers would probably ask the Truth Social developers questions under oath about how the platform was developed.
The evidence gathered during discovery is what the judge would use to decide whether a license violation occurred, and to issue an order.
So, the public evidence available at the start of a civil court case doesn’t need to support the requests for relief.