edit; didn't get all that was in my head out :-) So, it could be made up or support the fact that actual docs or good record keeping weren't a thing.
It's pretty strange, basically if you have a document with a bunch of numbers (say, some company's quarterly report), look at the leading digit of all the numbers. For some reason, numbers with a leading digit of 1 show up more often than those with a leading digit of 9 (i.e. 1,234,567 is more likely that 987,123).
You'd think there wouldn't be any particular pattern in the leading digit, I mean why should there be? But observational data seem to suggest a pattern.
So Benford's law can be used as a leading indicator of fraud. If you apply it to a quarterly report and there's an unusually high distribution of 8's, for example, then while you can't be certain that it's fraud, it might be flag to an inspector/regulator to take a closer look.
But when humans enter data, they tend to fake numbers with a uniform distribution - to appear more random. That's how you catch it.