tracking committer vs. author

I have noticed that when we pull changes from non-committers into our
repo, sometimes meta information about who committed the change to the
repo is included along side info about who actually wrote the changes.
 For example, see
http://github.com/grails/grails/commit/8ac450c37d16b0468ba0f92d3008968fd6a41a75
and note that graemerocher has commit privileges to the repo but
ihotary does not.  ihatory's commit was pulled in by graemerocher.

The commit at http://github.com/grails/grails/commit/ff770359d152683d5794887cd743a10ce7d04501 was also authored by a non committer. I pulled that change in myself this evening. Notice that there is no info displayed there to indicate that I (jeffbrown) am the person who pushed that change into the repo.

I don't know what was done differently for those 2 scenarios but both of those commits were authored by folks who do not have commit privileges to the repo at http://github.com/grails/grails/commits/master.

I don't think this is a github issue.  If I am wrong, please let me know.

If I want to track not only who authored the commit but also who pushed it into the repo (like you see at http://github.com/grails/grails/commit/8ac450c37d16b0468ba0f92d3008968fd6a41a75), what is the procedure for making that happen?

jb