He qualified this claim as a “cursory examination”. It’s clearly a comment about the quality of the data and systems. That this is the kind of thing that would be prone to fraud.
Before you hit downvote, please provide evidence that you didn’t hallucinate Musk’s claims here.
What proof does he (or you) even have that a COBOL system is particularly prone to fraud? The world’s most important banks still run many things on COBOL. Are you saying that bank mainframes are full of IT fraud?
Incomplete and inaccurate data is prone to fraud. Talking about COBOL is missing the point.
It doesn't mean the data is missing or inaccurate, any more than a null reference in Java means your program is going to segfault. It simply indicates that the data is not present in this scope.
If Musk was posting: "Guys I just discovered they have tons of null checks in their code here, that's obviously an indication of fraud!" — would that make any sense to you?