i get that everyone is saying "oh bullshit plotwist" and "its going to be a trainwreck" but just think about it carefully and it'll become clear that it can't be true what that fuckin guy is saying, why?
because from a writers perspective it doesn't make any sense, every festival chapter was made in a way that in the frist chapter it shows one quintuplet with a problem that agravates at the end of said chapter and in the next part the problem gets resolved and then kiss next sister, and it shouldn't be diferent this time, everyone is just asuming this is a setup for a shit twist but in reality i'm almost 100% sure that this was made to add to the problem that itsuki is facing that she is wrong all the time and that she doesn't fit in with the other sisters honnestly uesugi's father probably was about to say that the guy was a creep or something that liked the quintuplet's mother and that they should be carefull
though if that really is their true father i'm gonna give up on hoping reading a manga and it having a good ending i still have gakkou no juliet flashbacks