The fact that Thompson did the thing and bounced on a 3-hour endcap to an already 40+-hour-long story was reported in a profile on Thompson by The Athletic's Ethan Strauss.
"Thompson conserves his energy for what he loves, and he's always been impatient with any less than favored activity," Strauss wrote. "There was amusement in Warriors land when, with an hour left in the film, Klay just got up and left a screening of 'Avengers: Endgame.' The plot didn't interest him, not enough to demand that much time and attention."
Not everyone was cool with Thompson coming to the conclusion that Purple Josh Brolin hasn't earned what bloated Marlon Brando earned. Twitter users considered switching their NBA allegiances over Thompson getting bored. (Never mind that Thompson currently plays in the closest thing the real world has to the Avengers and even that can sometimes be boring.)