“So does an Etzba Ketana”[have the same halachos as an erva].
You refer, no doubt, to the ma’amar that if one gazes at the etzba ketana of a woman, it is as he if he has gazed bimkom hateiruf.
But that is not a halacha of an erva. I am referring to such halachos as a man not being allowed to say devorim shebikdusha
if he can see it, and a woman not being allowed to go out with it exposed – none of which apply to an etzba ketana.
A married woman’s hair, however, does have these halachos, just as does, say, a woman’s arm from the elbow up.