OP has interpreted this as not being g a problem. I'm looking out that if many people felt the need to drop the "I'm not interested in you, and I have a partner so back off" line then maybe there was a problem.
That's the thing with these kinds of situations, whatever the OP original intentions had been, they don't matter anymore as soon as the other party thinks he/she is being "hit on" and feels offended about it.
If the other party is actively looking to be offended, then there's literally nothing one can say/do to make it not worse, just walk out of the situation in silence and take a break.
If the other party is actively looking to be offended, then there's literally nothing one can say/do to make it not worse, just walk out of the situation in silence and take a break.