I’ll have to check but Korin said it as well.
But yeah I get your point. Like, going by the same logic, Roshi would need to have been suppressed vs Goku at the 21st. Honestly though, the prime Roshi might be a thing... But prime Roshi would have been able to one shot the mummy too... Like, The Mummy was said to "might be too much for the Goku from the tournament", so... Which version of Roshi would Roshi have in mind? One that was maybe, but not sure strong enough to one shot The Mummy? Lol.
Still tho, I'd say that statement is weird too. I also think the ones for Tao Pai Pai are. Which is why it's a hypothetical, a perspective... Which like the other one, will have its holes. I think though that the Roshi thing is an easier one to be faced with stronger skepticism given that Roshi was having a hard time in a tournament he wanted to make sure Goku would feel the difference between him and the opponents to the point he even used a kinda lame hypnosis sleeping to win... At least vs Grandpa Gohan, in the Baba tournament, it was an even but quick back and forth, one which Goku wasn't in trouble, like, almost losing to the point it'd be damn stupid if Goku hadn't used full power.