I'm actually skeptical about that. It certainly would be the "single most watched event in human history" among geeks interested in space, and probably among geeks in general and nationalists of the country that did the landing, but I suspect it's a biased projection to extend that attitude to all of humanity. Objectively, it's likely that stuff like the opening days of some war or the 9/11 attacks would be more watched than a Mars landing.
Apropos: Gil Scott-Heron - Whitey On the Moon (Official Audio): https://www.youtube.com/watch?v=goh2x_G0ct4