At least that's how the 3rd party recruiter told me he found me. It's possible he was lying and thought it would impress me (it did).
My profile is more active than most, but very far from rockstar.
Had to change my Location (or some similar obvious field) in my GitHub profile to "Recruiters FUCK OFF" before they took the hint. ;)
Thankfully, GitHub introduced some other way to signal if you are/aren't interested in getting a job (toggle switch?) not long after, which seemed to work.