What isn't true, specifically? I'm curious to hear what you think is "never true."
Have you uhhh, looked at the article headline? There's a pretty obvious and specific claim. That, as OP pointed out, has been claimed for many presidencies including the last time trump won.
If you read the article, how were you possibly confused as to what OP was talking about?
Anyway, like OP said, people have said they were going to leave if W won, if trump won in 2016 etc. Guess what? No real surge in migration either of those times. But sure maybe THIS time they mean it.