The difference is in fair use in Lyah's video (of Kelekelio's website), where copyrighted content is discussed and value is added to the original content through criticism.
If the other guy was to steal parts of videos without adding anything, then you could strike him for copyright infringement on youtube through a specific tool, and the channel may even be shut down.
The video above is just a copy of your format, therefore it is not a copy - paste or stolen content. You could argue that it's the same, however it is not. That is the basic concept of "reaction" on youtube.