Haha! I never call it a restroom either. I had always referred to it as the bathroom. although, I am sure that would cause some confusion too as you can, not always take a bath there. What do you call that room? When I was growing up, in New England my grandmother always used the term toilet, which, it was. My mother used the term bathroom and I answered everything.
I wished I had been there when you asked. I cannot believe (and yet, I can) that anyone would be so ignorant as to pretend to be shocked over such a thing. As if they didn't know what a toilet is. I apologize for all of them.