It’s not really a spoiler because in chapter 0 you see Guwon show up after you hear two people arguing and the guy talking about robbing them after he did something. Maybe he got confused with his memory and the disfigured rotting body and thought it was his dad…
I was thinking the same thing! Especially since in his dream his dad is in a darker shirt (not impossible but it gives them some separation). Guwon still could’ve killed his dad, like with the veterinarian’s family, but I think it’s more likely that the robber was the one to do it. (Or that could’ve been his mom, we didn’t see the speaker)
Spoiler warning oops
If you go to chapter 0 and 1 the guy laying in that spot was about to Rob him when Guwon came and killed him. We can’t see his face but we see the dialogue and the guy was going to try to rob him. Then he’s laying in the same spot as his “dad” but that’s doesn’t make sense….