@aubreyfromwheaton and @rc408: Air Canada's Aeroplan program does things a bit differently. They offer an "Air Miles" card. It's not a credit card -- it's just a piece of plastic linked to your Aeroplan account. Various retailers offer miles (at a very low rate, like 1 mile per $20) for shopping with them.
I'm almost certain this is what the OP is talking about.
The closest U.S. parallel is probably the various airline shopping malls, where you can get miles just for routing your online purchase (e.g., Barnes and Noble) through the airline portal. Doesn't matter what credit card you use.
So it's not like the gas station attendant was doing anything funny with anybody's credit card (nor taking miles that the OP was entitled to). He was just racking up (very slowly) extra bonus miles via Aeroplan's affinity program. Ethically questionable? Maybe. But very probably not illegal, since his actions don't hurt the customer.
Thank you for the clarification. I was begining to think I was missing something (or it was a troll post
)