If you were a designer, you would claim Dribbble instead of Github.
Either way, you would be delusional. Social is just a useful paradigm on the web. More and more products would use it as default. Just like every site now has a search box. Github also has a search box. It is not the most important search engine.
Google has a social network, and it isn't mentioned in the piece. But I'd bet there's little doubt Google is the most important search engine.
You're right about Dribbble, but I'd argue GitHub is for collaboration and Dribbble is for showing off. Certainly people collaborate on Dribbble and people show off on GitHub, but by virtue of how people actually use the platforms I think GitHub is more collaborative and more important (at least in the way the OP posits). Go to http://dribbble.com/, click the first thumbnail, and count the compliments in the comments.
Either way, you would be delusional. Social is just a useful paradigm on the web. More and more products would use it as default. Just like every site now has a search box. Github also has a search box. It is not the most important search engine.