I had the same thing happen to me...the pump shut off before I got my three cans filled (and car). I noticed the pump was at exactly $75, so I assumed that was the trigger.
You are correct. Many credit card companies have a $75 limit—they say in case your card is stolen. One truck stop near me has that policy, etc. I must go inside & give the girl my card & tell her to restart the pump & give me 2 receipts.