If Robert Pattinson had some real money and some fake money in his pocket, it’s at least fairly easy to see how a snafu of epic proportions such as this could perceivably happen.
While committing a federal crime is never a good idea, Safdie’s story makes it clear that even Robert Pattinson had no idea if he’d spent real or counterfeit money that day he was wandering the streets during his free time between takes.
The two directors also mentioned in their interview with Vulture that the props director really spent a lot of time on the counterfeit money and that even people with a keen eye could not easily tell real money from the fake money.