Even shoul NW have admitted to being oiver on Yichud (which seems to be a matter of some debate).
The very Gemora’s at the end of Kiddushin that make about the issur of Yichud make clear that being oiver on Yichud does not mean that someone was oiver on anything else.
In fact the there are those Shittos in the Gemorah that state one does not give malkus to a married woman who was oiver on Yichud since it may cause people to think that ch”v she was actually mezaneh.
So we have a clear cut Gemorah that states that proof of Yichud is no proof of znus.