Yeah, the article basically talked about Tor, but Dark Web is anything that isn't indexed by search engines, including, but not limited to Tor.
...And in the dark web -- they now have a Tor-friendly Onion address!
Facebook profiles that can only be found by using Tor (which I don't believe exist) would be in the dark web.
Maybe that's where the "Dark Web is bigger than the regular internet" meme comes from.
They somehow mix up the Dark Web and Deep Web (which are ill defined terms already) and combine their mythologies into one hilariously incorrect idea that there is a whole underground society 10 times bigger than the regular web.
More hilarious is how many of these charts put 4chan or the Pirate Bay just below the surface, as if they are hard to find sites. These diagrams are incorrect every way you look at them, besides maybe a "the lower you go, I'm implying the sites are less moral".