Hey Johnny,
You did get very lucky! Sometimes nice dragons end up in mom and pop type pet stores.
No one can really say if it is a "tiger" or not without breeding it. If you bred him to a non-tiger female and got strong barring with the offspring, then he is a "tiger". If you like the strong side bars that tigers produce, I would recommend getting a very nice female tiger to pair him up to. He deserves nice to keep the nice genetics going.
Good luck!