I think he means that he thinks his fishes's tail is going to get weak and start folding eventually but isn't yet. Some times it just happens in old fish but in your case it's in his genetics. It's not the worst thing ever it's just going to get worse in the fry if you breed him like I said before. Doesn't personally affect the fish and if he didn't have the drop tail he would be a 9/10 for sure but they can't all be winners. 7.5 is still way better than most. I'd be happy to have your fish for sure.
and just because he has a weak tail doesn't mean you shouldn't breed him. I'm just telling you most fry will have fins worse than his so they should be culled. Who's to say he won't have 10 amazing fry in the batch though? You won't know until you do breed him. Just don't expect to get 300 masterpiece fry out of this fish.