In principle however, this guy and his shop can eat a bag a d(irt).
But I understand logic of holding the tires. For the most part, agree with everyone else, I don't think it was unreasonable to contact Enkei directly... But did you try to follow up with the shop first? If not, that's the one thing I would have done differently.
Regardless, the guy is being over-defensive for his oversight. Granted, maybe it was just an oversight, or maybe he's swamped, but none of that is an excuse for failure, and he should be doing everything in his power to make things right, not end the customer relationship.