When they travel in time they're actually travelling to other dimmensions, so 2020  YTY isn't  PJG 's mother 'cause PJG's mother traveled to that dimmension back in 1990s and he was born there. Btw I can't help but feeling weird about their relationship.

I guess the director is really pushing it haha. I can't imagine the people on set, did they even cringe with those kdrama cliche moments between mother and son? HAHA