[Game Play] Zac's 2nd Q. The auto that isn't an auto?

So I noticed something really odd about this 2nd Q from Zac. It counts as an auto but doesn't count as an auto. Here's what I mean:

Zac builds . Revolver does not proc on Zac's 2nd Q when he slams an enemy champion if the champion is the one clicked 2nd.

Zac faces . Zac's 2nd Q does not proc vs Panteon's passive because it is counted as an auto attack.

So which is it here? Is it an auto attack that should proc revolver? Or is it a skill that shouldn't be blocked by Pantheon's passive? This is a little confusing.