In the OP, the first and third examples involve multiple strings, so I’d call it “strumming really fast”.
One of my favourite examples of it:
Ah, you beat me to it.
Notice also that he plays a left-handed guitar but strings it right-handed. And no whammy bar. For that reason I disqualify his music genre as “Surf Guitar”. “Instro Guitar” is more like it. Nothing wrong with that.
Some on-and-off alternate picking (starting around 29 seconds in):
Surprise, surprise - Contrary to the impression the name and album art gives, Daikaiju is from Huntsville Alabama.