fishy, maybe, maybe not, i mean, if it was bought at a pet store, there is no telling just how old they are.
See, what pet stores do (as far as I know), is that they put their bettas out in a variety. When they don't sell, they ship to another store, and they get other stores' bettas in that didn't sell, and they keep cycling them until they are sold, die etc.
My first bettas was a pet store, he lives nearly 4 years. The my second betta, also a pet store, i think was old when i got him, and died not long after, maybe a year or so.
If you buy from breeders, you can tell exactly how old they are, as the breeder will obviously know when they were bred. Pet stores, they just receive them from suppliers, and really have no idea.
but anyway, i am sorry for your loss. It is very difficult!