Thanks for the transcript.
"SYMINGTON: I think it was from another world. I've never seen anything like it, Larry."
So, Symington thinks it was from another world. That's not the same thing as admitting it was of alien origin. 
In other words, he has no clue what it was either.
He may be closer to the truth with his other statement:
"SYMINGTON: ...I don't -- I know of no other explanation unless a phantom stunk works have something cooking that we don't know about."
(I think he meant "skunk" works; transcripts aren't always perfect--like captions. 
)
There are lots of experimental aircraft out there that we never have revealed to us.
