If I understand correctly, the loosely knit online community started using the name well over a year ago. 4chan and advanced internet types, Twitter users. Breitbart has some older articles about alt-right.
I've seen the term used for at least two years now, maybe longer. However, it's mostly in the sort of social media and alt-forums that most FReepers have no idea even exist, which is why there is this sudden "discovery" of the term, which has apparently taken a bunch of people by surprise.
Vox Day has a fairly succinct summation of the general trend in what it means to be "Alt-Right" - What the Alt Right is