That bada is not actually an npc seems like retcon for the side stories. Maybe the author...

Yeah cuz literally the whole reason seongchun was left in the game is so bada the npc could escape in his place, if bada was a regular human from the start they could've all escaped only, theyre also being super vague on how long they were trapped/how, I guess they just wanted to get into the sides like an AU instead of cleaning up the narrative from the main story lol

I think it would be weirder if Pi Seongchan’s cousin (Bada) wasn’t a real person, all the real NPCs in the game were faceless (or bland looking) and didn’t talk or have a sense of self, which would be expected of NPCs that only play one role in a videogame. Bada on the other hand always had a face and could always talk to the others without issues. Bada himself says that they were probably stuck there for years and all of them very likely had their memories erased at one point since they kept putting in and taking out their tapes and repeating the cycle. Bada was probably always meant to participate since they couldn’t escape by simply not entering the town and driving back (I forgot what chapter it was but the road loops endlessly) which means that when Bada had his tape removed, his NPC version simply looped endlessly in the road, he was already stuck with the others in the game (and therefore he was a participant)

THIS! Also I think since he was saved instead of Pi seongchan, maybe he got real life by winning the game. So the game's description of his became reality.

As the comment below says, I think that he's an NPC in the sense that he was not a playable character. He's like an NPC who is programmed to do his own things, have his own life.