Not that it’s really important, but hobby bodybuilder here (don’t compete, just enjoy it as a sport). My father did the same. He has pics of him throughout the years and it’s for sure real. Every human adds body fat in different ways. For some people, it goes to their face. Others, stomach. It is definitely possible to be physically larger without having the same muscle mass. It would just mean his muscle mass/fat ratio was way way more insane as a young kratos.

Basically, you’ll have less veins/vascularity with increased bodyfat, but with the right genetics you can absolutely look way bigger. I mean it’d have to be a perfect storm if genetics for this to be the case, but it is a video game after all. Plus creators break canon logic quite often. Him stating it could’ve been an oversight. No biggie either way. He’s huge in every game