They promote the campaign on their site ( http://fontawesome.io/ ). A lot of people (including me) already visited the site occasionally to take a quick glance on the cheatsheet. I think that's probably where the most traffic originated from.

How do you know? Why is their site so heavily trafficked?

We posted the info he's referencing elsewhere in the thread. We're used on roughly 1 in every 3 new websites that gets made.

So you're like the Wordpress of icons.