If this is a purchased casino script, the owner may not know how it really works. It is possible that the seller just lied to him. He got the info that the script was provably fair and believed it. Now when he is asked to present evidence, he just can't do it and tries to hide it.
I highly doubt that it is the case as anyone with smart logic will try to find out about the important thing related to the product they want to buy.
In this case, having a casino is a business, gambling business so anyone who want to own a casino should not be that stupid to buy a random cheap script without doing researches.
I'm quite sure the OP know everything about the script including about the questionable provably fairness but he do not want to admit it.
Not necessarily.
With simple step-by-step instructions, almost anyone with basic computer skills can install a ready-made script on a hosting server. However, understanding the inner workings of gambling scripts requires knowledge of programming, programming language syntax, and math. Considering how much the OP struggled with just a simple task like editing a logo on a website, I believe he lacks the expertise required for something like this.
Regarding your statement that it's stupid to buy a random cheap script without doing any research, I completely agree.