From what I see, there's no further elaboration aside from those two pages, and there nothing suggests that the fireball is in any way comparable to his physicals, and here a positive needs to be proven, not the other way around. Our standard assumption for all magic and supernatural attacks is that they are separate from physical strength, requiring actual evidences to assume the two are comparable.
The demon very well be handling all his power, but nothing says it's physical power. Could be willpower, magic power, demon power, whatever power, we just don't know.
Unless we get some clear-cut evidences, the fireball can't scale to physical. And this ignoring how WWE wrestlers get consistently injured by things for which even 9-A is already a considerable stretch, let alone a huge gap like this.