The parent's story is essentially universal in the US and has been for decades.

Almost no convenience stores make money on gasoline, unless they're operating a special setup (the convenience store chain Sheetz for example has tried to build out their own gasoline business to cure this problem). There are a few routine exceptions, usually involving either some kind of rare location (eg right outside an airport exit, usually operating under a special arrangement), or a rare event (something that causes gasoline to be in unusual demand / limited supply).

When I did the books for a gas station in Canada it was similar. This was a franchise location as well, so they had the parent company buying gas for them.

Profit on gas was measured in cents per liter, with premium giving the best margins. And by best I mean $0.023/L or $0.087/gal.