No, Satoshi did not join Github 2 days ago. In fact, Satoshi does not have a Github account (at least associated with the name Satoshi Nakamoto) and he never used Github. The move to Github happened after Satoshi left.

This account appears to have falsely taken attribution for some of Satoshi's commits. This occurs because any Github account can add any email that they want to the Github account and Github will show any commits with that email as belonging to that account, even if the email is unverified. We normally keep the emails of Satoshi, sirius, and laszloh under this account: https://github.com/non-github-bitcoin. However I didn't notice that the satoshin@gmx.com email was used before in the commit history, so someone has claimed that as theirs with a different Github account. I'm currently talking to Github about this and hopefully it will be resolved soon.