I doubt very much that SE is actively scanning for youtube videos to block and close their accounts. It has to be youtube's automatic system who is doing it:

A lot of info about how Content ID work and how to fix it:
http://www.youtube.com/watch?v=slgldWAsB0M

Some random guy explaining how the gaming community has been affected and how some companies have responded:
http://www.youtube.com/watch?v=3WrPR7BXVoI