Not sure if Caribdis was involved with OIAL incest, but for me UNLESS there is a very good story reason: A kid staying with an older female roughly 20 year older and some younger females around his age, screams incest. There is no plausible reason without a decent explanation or background story why that would not be meant as incest. That is why I always play a game that looks looks like that with an incest patch.
You do get games, where the dev sets out a very good reason, and it's actually part of the plot, that an MC would not be related to the females. In that instance (i.e. "Where the heart is") I do not like to play with an incest patch.
TLDR, If it walks, looks, sounds like incest....It's incest.
OIAL felt like incest, so that's why I played with the patch.
I don't particularly love incest games, but I do like to play games the way it was intended.