Hate to jump on the cynicism wagon, but, it is a track tested theory. Videos with live action people thumbnails do better than drawn images or non human objects, out of those: attractive females do better, out of those: the ones that show a little skin do better. Just the way it is.
As for when some generic obnoxious kid video randomly gets 100,000,000+ views out of nowhere.... that is a strange phenomenon...LOL...honestly, i would write it off as BH style IM people having a hand in it, but, if y'all don't know, then, it truly is a mystery.
One theory is: its a fairly known practice for some tubers to use bots and sock accounts so they never have any period where a video has no views/subs/comments.
I guess sometimes they may accidentally buy too many views and you get those occasional vids that inexplicably have viral level numbers when almost no one at all has seen them.