Or maybe by blocking it during the timeframe they did, they have accomplished their mission and there was no further need for blocking.

I sincerely doubt github is at all important to China.

again, then why did they unblock it? it is important, we're in a new paradigm for software where developing in the open leads to higher quality software written faster than previous ways

It's hardly a new paradigm, it's just a place with a lot of software that you'd otherwise have to write from scratch. It's merely software development catching up with everything else.