It's a common manga trope that bitches who sleep around and have a goody-two-shoes guy with them end up crawling to the goody guy if the other ditches them after hearing they got knocked up.
It's a very common thing in manga, if you get around you'll get used to it to the point of immediately knowing she's lying unless the author makes it an important event that MAY yield in an actual child of the male character in question being on the way.
If it's only mentioned, as it is here: The bitch is lying to avoid ending up being a single parent or avoiding 'bringing shame to the family' (which is sadly still a common thing in asia..).
As it is here; it's an ignorable event.

Wait wait wait a damn minute. Are we bypassing him having a possible kid with the woman??? I don’t understand. Lmao. She really pulled a Maury and they just left it like that??