Usage doesn't necessarily denote that heating isn't an issue. Essentially what happens is when your OS detects that you're trying to start a fire and will throttle down your CPU to keep it from bursting into flames. The main thing being that you *would* see high CPU usage after prolonged gaming session because your OS would slow down the works a bunch, but once you relieved the stress it would stop the throttling and usage % would fall, potentially substantially. It's always good to have a clean - I shoot for once a month.
Monitoring software is freely available and it's good to have a peek every once and a while just to make sure everything is in tip top shape - like OHM or CoreTemp or even ol' Speedfan.
There was a case on this forum AGES ago where Crespi was having some pretty intense performance issues and discovered that his manufacturer (MAC) had poured a 1/2 pound of thermal paste onto his CPU, causing massive overheating and shmoo to go all over his MOBO lol.
It could also be a background application doing something really stupid, or malware of some form or another sucking up CPU intermittently.
I couldn't really see that well in the video as your FPS was pretty highly variable and it did dip to ~80 that I could see a bit, but it's also possible that you're on some kind of shared internet connection and it's experiencing intense momentary lag (like when a video buffers), but I didn't notice your ping # jumping up a ton (which it could in such a case) - though if you're on wireless you could get similar hang if somebody nearby used a microwave or a cell phone.