They might have been passing also. I am not trying to talk down to you; but it is a fact sometimes. It was survival and made sense to some people. It meant they didn't have to put up with certain indignitys that people suffered in those days and then you had the Census takers or enumerators who took it upon themselves.
They your people that is; might not have had a chance to see the census in some cases. In some cases. They better not question or ask what was down.