The face of the girl on the left at the start in the first second should have been a giveaway.
No one is looking at her face though, they're looking at the giant hello kitty train. And you were only looking at her face because you were told it's an AI-generated video. I agree with superfrank that extreme skepticism of everything seen online is going to have to be the default, unfortunately.
Hard to not discount that as a compression artifact.
Just like all the obvious signs[1] the moon landings were faked.
[1]: https://web.archive.org/web/20120829004513/http://stuffucanu...
One thing that's not intuitive to spot but actually completely wrong, is that in the second clip we're apparently inside the train but the train is still rolling under us.
Also "HELLO KITTY" being backwards is odd - writting on trains doesn't normally come out like that eg https://www.groupe-sncf.com/medias-publics/styles/crop_1_1/p...
My intuition went for video compression artifact instead of AI modeling problem. There is even a moment directly before the cut that can be interpreted as the next key frame clearing up the face. To be honest, the whole video could have fooled me. There is definitely an aspect in discerning these videos that can be trained just by watching more of them with a critical eye, so try to be kind to those that did not concern themselves with generative AI as much as you have.