There's no such thing as a roider belly. If you're referring to insulin belly that some current top level bodybuilders commonly have, then thats not it, thats a thick abdominal wall, likely combined with a carb load which may cause his belly to look bloated.
He would be on some form of PED's though, wherther it be roids, GH, or other things. His opponent may look like hes not on anything, but all top level athletes are on something.