The literal answer to you question is "yes" because it's unprofessional to do anything your employers don't accept. They get to decide what's "professional" under their roof, and professionals abide by the rules.

That said, in the uncritical context described, I think they are full of it. In casual conversation I find it awkward (if not rude) to force a less familiar language on someone. I think you were pragmatic, polite, and welcoming, but it's my luxury of detachment that permits my view; as an employee, you don't get that luxury.

The literal answer to your question is "yes" because it's unprofessional to do anything your employers don't accept. They get to decide what's "professional" under their roof, and professionals abide by the rules.

That said, in the uncritical context described, I think they are full of it. In casual conversation I find it awkward (if not rude) to force a less familiar language on someone. I think you were pragmatic, polite, and welcoming, but it's my luxury of detachment that permits my view; as an employee, you don't get that luxury.