Would ground "popcorn meal" differ from regular corn meal?
Interesting question. so I pulled out a hot air popper (you wouldn't want to use a oil popper to try this.) and put some popped dry corn into a food process and let-her-rip. I wouldn't call the results "masa" but it might be usable for an ingredient in a breading.

I call your attention to the book "POPCORN". It has a nice collection of recipes which include popcorn, and in no case does the author suggest reducing popcorn to corn meal, so I suspect the answer is, "Yes, ground popcorn meal would differ from ground corn."