When it's a grey area as to whether it should be taken literally?

So my mom was asking a bus driver something about how far she'd have to walk to get to her connecting bus. He said the bus stop was about a 10 minute walk. For whatever reason the answer surprised her and she said "fcuk off?" He replied "fcuk off" with a smirk, as if to say "I'm just giving you the information". My mom laughed. But at the end of the interaction she said "I wasn't telling you to **** off" and he said "I know".

Now is what my mom said the sort of thing that someone could potentially say to have it both ways? As in act like oh that just something that people say and you're not meant to take it literally, but also vent a frustration or blame onto the other person?

I must watch my mom more closely. I think she'd usually say "no way?"