I've written extensively about this tactic for more than a decade. To sum it up, it's not about sources. It's about putting you in a defensive position by calling for sources, which forces you into a position where you have to prove empirical truths, which creates an impression that the truth isn't empirical at all, when it is.

Then they refute those sources no matter what, say it's wrong, try to say it means something else, or sweep it under the rug entirely and make a straw man argument that puts you on the defensive for things you never posited in your side of the argument.

This is where they get some people, because they create a straw man argument they're right about, but that was never posited and has little to nothing to do with the original argument. But they put it up as a point on the scoreboard for themselves nonetheless. It's like if the losing team at a baseball game in the last inning suddenly brought out a basketball hoop and made a 3 pointer, then claimed they're ahead in score.

By arguing like this, they automatically create a facade of putting themselves at the top of the hill on their high horses, making it an uphill battle. By making you have to prove you're right, they're creating the facade of them being already right and you having to prove them wrong. And at that point, all they have to do is merely indicate you've failed, giving the appearance that they are on the right side of things....when they never had to prove anything about their position at all.

Don't fall for those traps. You won't change their minds. They aren't there to have their minds changed, they're there to waste your time. And even when you start getting leverage, they'll delude things to the point where it doesn't matter who is right or what the original argument was anymore, because they want to make thing contentious and the whole argument look tainted. If they can't win, they don't want it to look like you've won either.