I have had to drip some fish for hours. One local store keeps salinity at 1.013. I'm not exaggerating. I've never had this issue. I'd say too many fish too fast.
In this case though you should have a qt setup at 1.013 then only temp acclimation is required.
I do agree that Id hope you'd be ok with an hour acclimation but anything over 30 minutes and you are playing with fire. It certainly could be a factor in this case.
How far away from the LFS does the OP live? Was the bag airtight?
Too many fish too fast is also a reasonable suggestion as the culprit.