What a near nightmare!
Good thing you knew some French to get that map and back on your way. More people in EU (and Quebec) know some basic English than they let on. Wonder if that happened to you as I assume the person at the mini-mart surely knew you spoke something not FR.
When in Quebec, referendum for separation was in hot motion. To certain FR people, anyone who spoke EN was presumed one of those CAN-EN bad guys still wed to the British ... and not conversing in EN under any circumstances was their weapon. For most of the CAN-FR I met or dealt with (tickets, food etc) were civil, pleasant - sometimes we would speak Franglais to each other.
It's like that in Catalonia in Spain, especially in Barcelona. If they know you live in Spain, and you speak in Spanish, they will pretend they don't understand it, but if they know you are a tourist speaking Spanish, they will speak Spanish to you.