Language evolves.
Party has been used as a verb as far back as I can remember and I have been here for over half a century.
Looks like I am right.
http://oxforddictionaries.com/definition/american_english/party?region=us&q=party
Well I've been here a little longer than that and I have a very good memory. Party started being used as a verb in the late sixties when drug use went through the roof. Although legal, I also include alcohol as a drug. Back then, the mere act of being sh*tfaced was known as partying, even if you just laid around like a zombie.
If you can provide earlier evidence via books, movies, tv shows, etc. I'll gladly change my stance. Until then I'll stick with my 'nincompoop' analysis.
BTW, your link neither supports nor disputes what I say.