No, it's called lore, it happens in most games that attempt to put in some form of story. Any humans who lived on the island are presumably dead considering the buildings are all in ruins, there would have been nobody to teach human concepts to the androids and so they are left with their base programming. The reason they don't react at the medium values of humanity and instead react at the earlier part of the high values is because they still aren't to the point of reacting like a human would. The 100 humanity threshold represents the point where they learn that it is not okay for total strangers to just walk in on you in certain situations, those situations being when masturbating, on the toilet, or in the shower. I will admit there was one they missed that they did implement in Koikatsu and should have in this, during lesbian. The androids don't react in lesbian no matter what, you can get right in their faces and they will continue as if you aren't there no matter the level of their humanity stat. This is most definitely an oversight canonically and technically speaking as it leaves a single situation where they don't react that would technically count in the same category as another where they do react. This is contrary to reaching the point in canon where they have learned how to react and it is also leaving an inconsistency from a technical standpoint.I think this is just an excuse by the developers who were lazy to script more than one type of reaction to certain things.
What you say would make sense at the medium values of the humanity stat.
With high values there should be more possible reaction types.