If you look here (current page for earliest commits in Bitcoin),
https://github.com/bitcoin/bitcoin/commits/master?page=289
you can see that commits done by sirius-m are attributed to Greg Maxwell.
This does not seem to be a problem with the import from SVN, as the committers show up correctly in a ‘git log’. This also matches the info in the old SVN (still available on sourceforge).
Rather, it seems to be an issue or a misconfiguration on github.
I didn’t check whether there are more issues like this.