As developers who start writing big servers learn, scale matters. Crap you'd never think twice about when running a script on your workstation will bring your entire service down. There's 7-ish billion people in the world. Entire industries live in situations you've never experienced. There's plenty of scale that all sorts of weird things really do happen to someone, somewhere in real life.
I don't find this all that hard to believe. To be honest, I'm not even sure what you're finding hard to believe. What exactly is it? That a law firm could be that clueless about tech? That someone would discover this opportunity and simply milk it for all its worth? I don't find any aspect of this story particularly hard to believe. I'm sure this story is happening at least a thousand times over somewhere in the world in some form.
In fact I'd bet that if we could investigate carefully enough, we'd find someone out there who has at least three of these jobs with different companies. Someone who blundered into one of these, figured out some useful pattern, and figured out how to do it systematically. Probably as a contractor.