Did I just get screwed by eBay as being a seller, forced to refund buyer after he sent me an empty box?

Unfortunately, you can't really sue him because as far as I know, you have to file in the state he lives in. So it's not worth it. You could maybe have your lawyer relative call him and bluff that he's gonna sue him for damages, and your expenses, such as flying him to the district he lives in, to file in small claims court. That may shake him up, however, as an attorney, he may not do it. You can try the bluff with someone else, though.