The difference being the ability to tell if a spell was obviously cast, i.e. no means or attempt to hide it, visible components, etc…vs identifying exactly what spell was cast. It is completely reasonable to have just about everyone in a magic fantasy setting be aware of magic existing and being able to say, yep…that person just cast a spell. What’s a wildly over-the-top suggestion, as made by the poster I was responding to, is that everyone in the world could make a check to identify exactly what spell was being cast.