Ive experienced the "seeing faces in things" for about 3 years now, but I did not have this at the beginning of my dp 7 years ago, which is kind of disturbing. So like you, I also started to have it later on I guess. This here describes it, but I think I read somewhere else that in regards to mental illness, it actually could be a part of psychosis. I think even a different term was used for it. This is all I can find on it now though. https://en.m.wikipedia.org/wiki/Pareidolia
Pariedolia can happen to anyone, but in the context of mental illness, I think its related to dissociative and psychotic mental states if its happening very frequently and alot more strongly.