You clearly didn't understand what I meant with "time travel isn't real", this game is, like most games, based on the real world, right? where people don't believe time travel exist, because it's a "sci-fi concept", when you see someone similar to a person you knew 20 years ago, your first thought isn't "wow, time travel exist" it's "could be related to this person", that common sense + the fact that it was 20 years ago + the fact that there are literally no photos of that person... makes sense people don't connect the dots and think MC is the same guy, there's literally an excuse to explain everything, even Olivia have an excuse, so far MC had the biggest impact in her life and she probably suspect, but there are other more logical explanations, like for example thinking this guy also impregnated her sister and that's why the MC and that guy from 20 years ago look alike.
Again, give the game time, they will probably develop that more in the future, someday every present character will know his secret.