Yes he is, Casimero threw everything but the kitchen sink there were rounds where Casimero stops throwing punches because he couldn't figure out what combination of punches should he throw to knock Nghitumbwa out, Casimero resorted to holding in the latter rounds because of fatigue.
What we've seen here is Nghitumbwa is a tough guy who can take a punch and Casimero should have more tune fights before fighting for a world title he is out of the ring for too long before this fight so there was little bit of rust and fatigue easily caught up with him.
It looks like this is the answer to Casimero's request since he stated that he was quite not satisfied with the fight against Akaho because it lasted only in 2nd round, and he wanted to be satisfied on this fight, and yes the fight goes the long way into the hand of the judges. I bet this time Casimero is fully satisfied with the length of the fight.
Nghitumbwa is surprisingly tough since we had compared this guy against Tete which lead us to think that Tete is way tougher and better than NGhitumbwa but it looks like we are wrong with our assumption. Regardless, Casimero wins and I also agree that this is a good opportunity to hunt boxers on the top ranking replacing them in their rankings.