I think that the responses so far ignore how youtube content ID works.
So, fair use is a legal defense, not immunity from content ID. So, the way Youtube content ID works is that it's mostly automated -- if exact pixels or exact audio soundwaves match something that's in the automated system, then the system should flag that as a claim...but only certain copyright holders (usually, the largest/biggest groups) are in this automated system.
I just looked at a few of his thumbnails and went into one random video, and I noticed three things:
1) he's usually ripping smaller youtubers. He's not, say, reposting a professionally done movie or music video. So, those youtubers probably aren't in the system at all.
2) he's usually pointing a camera at the other video...He's not, say, downloading the video file and then reuploading it. So even if youtube does have those videos in the system, it wouldn't be a pixel-perfect match.
3) He usually doesn't include original audio from whatever he's taking. So the sound won't get flagged automatically.
Again, you should think about it from this automated vs non-automated perspective. If you think fair use can make you *immune* from content ID, you're going to have a bad time -- at least theoretically, yes, companies should be evaluating for fair use before putting out content strikes, but there's not an easy way to *automate*, so that's unlikely to happen.