They did this on Mythbusters and showed it was possible.
> Yet, it seems that until a couple of years ago there was no proof that any person had ever broken glass with his or her voice alone.
> Then in 2005 the Discovery Channel television show MythBusters tackled the question [...]
Considering that we have had witnesses reporting that tons of times in the last 200 years, and written records of such acts (by journalists), and everything, this is a peculiar version of "proof".
I agree that a Mythbusters finding may not be proof of the highest calibre but they do go through a lot of effort to avoid false positives/negatives.
They might not have been aliens from another planet, but UFO just means unidentified flying object, of which tons exist.