It just seems really weird to be able to correctly say that A caused B when, in fact, A had nothing to do with B. If that doesn't seem weird to you, then O.K.

This point is completely independent of whether causation is "in the mind" or not. Also, correlated things do have something to do with each other (by definition!). What is at issue is whether this something is "out in the world" or "in your head".

I think that's unclear; I side with those who think Hume was arguing for causal skepticism rather than some sort of subjectivism.

Right, there is probably no consensus on Humean interpretation. In any case, Hume would predict with near certainty that a billiard ball that was struck by a second billiard ball would make a sound and roll away in regular manner, just the same as you would. But since he doesn't need this "causal necessity" thing "out in the world" somewhere in order to coherently make the same prediction, your web-of-belief real estate seems to have lower rent than Hume's.