You should be telling yourself this, not me.

The other person claimed all the good teachers were online. Yes, we should ask for evidence for this. But did your original comment do that? It didn't.

Instead it made a claim that the good teachers are not on the internet. This is also making a spefific, very broad claim, which we should also ask for evidence for. Which is what I did.

It seems you're under the mistaken impression that the "neutral" stance, that doesn't require evidence is a claim like the one you made, that (if the original person's claim was X) "not X" is true. But the only stance that doesn't require evidence backing it up is the agnostic one of "I don't know where the best teachers are these days".