I won't watch the video as I don't have time at the moment (but I'll check it out in the next days). But even so, MD is a better SEO than I am so you should probably believe him
This being said, I'll still answer your question, just for fairness:
this should only matter if your site is new and didn't have any backlinks yet. For fresh sites without backlinking history link velocity is important indeed. So yeah, 100 links in 20 days is too much if your site is not established. And if it's already established (has age and prior backlinks) then I'm not sure where the problem is, sorry!
well, you've got your answer then
it's true! And yes, I did experience it myself. I've built 100s of links to a 1.5 month new website in like 10 days, and one week after the important backlinks has been indexed my site had gone from pages top 50 to nowhere
Anyway, most people agree that you shouldn't disavow the links which was my initial response, too. But you're almost certain that the links are the issue, so I don't know what to say in this case. You have a tough choice to make