Perhaps it was a joke…or perhaps it is severe backpedaling now that he’s on record.
There are quite a few countries around the world that have made statements that there are indeed UFO (not necessarily of the alien variety), least secretive is France who released a bunch of documents in I think it was 2007….but there is a whole list of other countries who have participated in the releases of documents on the subject.
http://www.disclosureproject.org/countries-releasing-ufo-files.shtml
I personally, tend to believe that there is something going on….there have been far too many credible witnesses over the years, people who potentially gain nothing but could lost everything because of their testimonies…pilots, astronauts, etc.
I’m sure a good portion of UFOs are indeed experimental aircraft…but some of the accounts of seemingly physics-defying maneuvers makes you wonder if that is within our own capability.
I don’t necessarily think they are from another planet….a more likely scenario would be ourselves from the future, or from another universe entirely…*shrug* who knows…I don’t think they were all just “swamp gas” lol.