I don't think it's as black and white as you say. "I won the presidency" could, in theory, be a true statement, even if it comes before the counting is complete and we haven't yet determined its veracity. "There was fraud" could, in fact, be true, even if the evidence to prove it is not forthcoming.

Ultimately, Twitter censors things it doesn't think are healthy for its platform. I think that's within its rights, but I don't think it's by any means objective.