Not sure I'd call it nonsense.
Nobody can say for 100% these things are aliens, but the evidence that UFOs are real and unexplained is incontrovertible.
Governments have had their smartest minds investigating these things, yet we're being told that they have no idea what they are or their intentions. We also know that governments have been covering this up since the 1940s. Not just the US government either. Winston Churchill covered this up as well as he didn't want to cause a public panic, which in the mid 20th century it absolutely would have caused a mass panic.
Declassified files from the last century show government concerns over UFOs, and reveal that Winston Churchill ordered a cover-up to prevent "mass panic".
www.bbc.com
It's absolutely not foreign technology, so that raises the question of what are they?