Hold on. Your first video is indeed a rolling shutter artifact. But your second video never shows enough of the string to see the harmonics. When you (for example) pluck with a finger on the 12th fret, you absolutely do have a real physical squiggle vibrating in the string, with one node and two antinodes. With a 7th fret harmonic, there are 3 antinodes, with a 5th fret harmonic there are four. There are squiggles, and you can see them with real slowmo.
You can actually see the node with the naked eye. No need for slow mo: the stays put while the rest of the string looks like a blurry mess.
Yes, I think that with all these videos what you actually see is aliasing...