Reading your posts I think the issue here is there is a backstory (unknown to your neighbour).
Your DH likes role play and sexy dressing. Youre aware of that (she isn't).
You state she is attractive?
I think this highlights your insecurities.
I've had many drunken nights with my friends at my house talking about their latest hookup and other sex chat with my DP present. I've never felt threatened.
However if I felt my DP could be attracted to my friend and my friend started to talking about a kink my DP is into then yes I probably would feel a little threatened.
However I wouldn't be mad/annoyed at my friend because'
-she doesn't know my DPs sexual pretences so that saying what she said would set him off.
- she wouldn't know or believe that my DP could potentially be attracted to her.
So I think your neighbour really isn't the issue here.
I think there's insecurities on your part that have been brought up. Do you not feel he's fully satisfied in your sex life? Are you not fully into what his sexual preferences are, and having a woman who is into it and talking about with making you feel insecure that they could have a potential sexual 'spark', both clearly being into the same things?
Of course there is now the open knowledge to you that she is into his sexual preferences and he has made it known he also is too. So now that's out there.
If he was into something completely different like very large women dressed in bikinis then you probably wouldn't feel threatened by what she said knowing your DP would have 0 interest and probably just laugh it off and think nothing of it. But because you know there is the threat of the 'spark', its got your back up?
But remember, she has 0 idea that he happens to coincidentally be into what she was saying and that he has the potential to be attracted to her. So it wasn't intentional on her part.