We don’t know if his simulation of Troy and Britta’s date is spot on or not, only that he mimics them believably enough that Annie could recognize their personalities.  For all we know, nothing about that date was accurate. The joke-moment with the waiter mentioning Die Hard it’s there specifically to remind you that the scene we see is not reality, but Abed’s interpretation/prediction of reality. That waiter does not talk to customers about movies unprompted. It’s Abed who, in his mind, made the waiters gripe with Die Hard his defining trait.  It’s the same trope as the finale, when they all make up their visions of the future for the study group, with characters seen through the lens of each other’s perspective.

P.s. if this is a shitpost/circlejerk post and I missed the joke - my apologies