Not sure if bug or not. I've noticed that the admin quick search gives not so relevant results at times. If you will search the word: "message", in order to find that template, it won't show up in the results. Instead, you'll see other template results which contain that word. I think that template name which start with that word, would be more relevant than strings that have the word in the middle/end. You can test the same with the word "post".