Go to the suggestions tabsuggestions tab on your profile page. This lists all the suggested edits you've made.
If you click on the suggested editsuggested edit link you'll see your edit and how it was resolved.
In this case the reason was:
This edit is too minor; suggested edits should be substantive improvements addressing multiple issues in the post.
Basically you only added one word to the title rather than looking at the whole post and correcting other errors. That, coupled with the fact is was an old question were the reasons I would have rejected the edit had I seen it.