“They” being someone writing under an anonymous pseudonym with no connection whatsoever to Bill Waterson, who made a poor-quality 8-page “book” just to try to fleece some rubes.
In BATMAN BEGINS, Christian Bale’s first outing involved everything you’d maybe now expect: seeing little Bruce’s parents getting brutally killed right in front of him; seeing our hero, now all grown up, in his first masked meeting with Jim Gordon; and plenty of grueling training in between, as well as the public’s reaction to the debut of The Dark Knight.
In another Tarantino movie, Once Upon a time in Hollywood, it is strongly implied that Cliff Booth (the stuntman played by Brad Pitt) killed his wife. Tarantino’s novel of the movie confirms it.
Also, we have the famous monologue from Jaws, where Quint tells the story of the sinking of the USS Indianapolis after delivering the atomic bomb.
From The Empire Strikes back.
Princess Leia: I thought you had decided to stay.
Han Solo: Well, the bounty hunter we ran into in Ord Mantell changed my mind.
Apparently, that story was told in the Star Wars comic strip, but that’s not canon. I’d like to see what happened there.
While being kidnapped, and not knowing exactly what’s going on, he says "It wasn’t me, it was Ignacio. Did Lalo send you?”. At the time (even to the writers, I think), it was just a throwaway line. However, 6 years later, Better Call Saul debuted which very prominently featured two characters, Ignacio (Nacho) and Lalo.
In Waiting…, they actually show them (I’ve never seen that film, but I just saw a clip now)…but I’m almost positive the joke was first made (as a passing comment) in Annie Hall. (I could be misremembering).
Not a movie, but a Simpsons episode: in the New York episode (I think now kinda banned because the Twin Towers played a big part), Barney one night at Moe’s is the destined driver and drives Homer and the rest of the gang home in Homer’s car. He goes missing for a few lost weeks on a bender and returns home without any memory of what happened, but it turns out that he left Homer’s car in a no-parking space just next to the Twin Towers. I’ve always wanted to know what happened to Barney in those few weeks.