I'm doing the trans-math here:

So, FtM = female trying to act like a male.

"You will never be a woman" is a statement you use on someone who looks like a male trying to look like a woman.

This female trying to look like a man takes it as a compliment that they're told they look like a sad excuse of a man...trying to look like a woman.

Now, I'm probably overthinking this, as based on the cartoon avatar I don't even know if pictures were seen, and it may have just been a random insult...but it's still a weird flex to pretend to be happy about that.

I don't care if you're "FtM" or "MtF," being told "you'll never be a woman" is nothing to be proud about. Yeah, that just means you're a freak, and should get help. That's not "gender affirmation," you sad excuse for a human.