Hello Skye,
Sorry, but a Windows Update WILL NOT revert a upgraded Windows 7 back to Vista like that.
It sounds a lot more likely that the computer store messed up and did a factory restore from the recovery partition on your computer, and that is what restored Vista since that was on your computer from the factory.
If this is what they did, then that most likely may have also wiped out all data that was previously on your computer for good.
I wouldn't let them get away with trying to cover up their mistake with a BS line about it being caused by a Windows Update.