Check this record of Nghitumbwa https://boxrec.com/en/box-pro/814162 he didn't face yet the same caliber as Casimero.
So this will be a tough fighter like Casimero and provably he will be tested here if he's knockout power is really good or maybe Casimero he will be dominated by the champ. Although we don't know if we can see an impressive match up but still its good to watch since its still Casimero will fight against a knockout artist.
but for me personally ? this is not enough to bring down the champ from Philippines , this will be a big step for Him if he can knock Casimero Down (wishful thinking)
But i'm confident that Casimero won't let himself be defeated by an unknown boxer because if it does, as you've said, it's a big step for Nghitumbwa's career.