xkcd

Yeah, that's him. He's listed in the credits:

Narrated by and based on "What If" by Randall Monroe

I would never have shared it if it were just some random person freebooting his content.

You do make a good point about the footnotes and mouseover text. I wonder if there would be some way to weave them into the videos. Perhaps inserting them as a single fleeting frames? It's a shame YouTube got rid of annotations, as the "hidden annotations" seem like they'd be a perfect fit for this.