Here is their landing page when they first launched: https://web.archive.org/web/20081111061111/http://github.com...
Notice how the entire page is making you believe they are building a social coding platform? That's no accident, "Social code hosting" tagline in the logo included.
Yes, we know git repos get used by clusters of people. That is not the accepted meaning of "social network."
Nobody is posting the news, their kids, or joining film groups on Github.
A pull request with the requisite commentary/discussion is absolutely a social phenomenon. Even simply pressing the approve button or the star button is a social act as it is a transaction involving more than one person.
And if you’ve never encountered the toxicity commonly thought of as only belonging to “social networks” in a PR or issue, then lucky you.
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> explicitly for social coding
Using source control is not "social coding." You're stretching that word far past its actual meaning, in the effort to make a point.