Tbf I’m not sure which part of the scenario could be said to be to blame for him being excluded. But I think it’s fair to say that had he not expressed an opinion that went against the school’s view of what’s acceptable, he would not have been sent out of the classroom.
That could be said of anything though. If a pupil gets sent out of a maths lesson say, for continually trying to argue with a teacher about Brexit say, (when said teachewr has made it clear they do not want to discuss it and wants to just get on with the lesson) well that could be presented as kids being excluded for questioning Brexit.
I mean, surely anybody sane can tell children that they can't biologically become the opposite sex?! Even if they do transition properly when older, it doesn't mean "tada, you're now a biological woman or man?!"
The only immovable facts are that you cannot change chromosomes, and no medical procedure will convert an XX to an XY and vice versa.
The rest of it is ultimately about wordplay and the meanings we attach to concepts, and is a matter of ideology.
In otherwords, no-one should object to telling children that you cannot change chromosomes, but telling them that they cannot become boys / girls / other is an ideology which can be as contraversial as any other can be. Depends on the zeitgeist I guess.