git: Why "Merge branch 'master' of ... "? when pull and push
When you did a git-pull, modifications from the remote branch were merged into your local branch. The automatically generated commit signifies that.
Merging could have resulted in conflicts, which would then need to be resolved manually. In your particular case, this did not happen and git could take care of everything.
If there could be changes by others, it might be a good idea to do a git pull --rebase (i.e., add your new changes after the remote changes; this might find conflicts you'd have to resolve) and then git push the result. Be careful, this creates new commits that did never exist before (as does any history rewriting), but it gives a clean, linear history (no tangle of merges)