I am not sure, it could be a crowntail. Some of his fin may not be as grown out as the other parts. He could have just had some previous fin damage. Or the other thing I can think of is maybe he has some weird genes. Like maybe his father was a crowntail but his mother was a veiltail.
I hate it when fish stores don't have the correct set up for bettas.
Our local maidenhead aquatics has a fantastic betta set up, where they have their own small tank with filtration. Rather than being picked on in a tank with Gouramis/ mollies and other incompatible tank mates.
I'm sure it would be in the lfs interest to house them correctly, I really don't know what price they buy them in at, but surely they want to sell them at their best rather than totally fin nipped and dying
There used to be another location nearby of the same shop and they sold the bettas and this one didn't. The old shop had the right setup. The shop left doesn't sell them that often and could make a bit of a better choice for housing them.. like they have a plants display with the odd fish as well as a couple of display tanks that are running with not that much swimming around.