The difference is that velvet is not skin. On a button buck the buttons are still covered with true skin and hair. On a buck in velvet the antlers are protruding through the skin. Don't know what part of Texas you're in but I bet he won't be in velvet long. Most of ours went out a month ago. He may be the odd late one that TPWD didn't count on. They are usually in velvet one day and out the next.

There are a couple of rare exceptions to what you are talking about also, and they are hermaphroditic deer, antlered does, and castrated bucks. Some of these can grow antlers that are never shed, keep growing, and never go out of velvet. Racks will often be small and mis-shaped also.