Possibly the values are all with range. It was just that this operation only worked on elements that were a subset. No amount of validation will catch that error.
You could feedback a clarification, but if that happens too often nobody will double check it after they have seen it over and over.
That is rather offensively narrow-minded to think that "regular people" don't also enjoy those those movies. That simply having a job or hobby related to STEM somehow does not make you a regular person.