Is it rude to have a conversation in front of someone in a language you know they can't understand?

I was at an event the other day, and I had already met this woman. She knows I don't speak Polish, and she is talking with her colleague.. who was a speaker at the event, so I know he speaks English.. and we're standing at the same table at the reception and they're talking to each other in Polish... But then we ended up having a really LONG conversation later... which was probably a waste of my time because I found out 80% through the conversation that she has a husband (she didn't have a wedding ring on)... But anyway, that bothered me.

Is it rude to have a conversation in front of someone in a language you know they can't understand?
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