This video seems like extremely unserious clickbait. Spending 5 minutes speculating about a single data point that it took a minute to not actually explain? Just grist for the endless content mill.
A drop or plateau in searches can mean, among other things, that people are finding out about a thing without having to do a super-beginner, bad-at-internet general Google search. Do people who want to know about the next Marvel movie punch "MCU" into Google and let'er rip?
Stupid video premise is stupid.