He didn't mention that he touched it at the time. Why would that not be in Halt's official after-action report?
The lighthouse it more implausible considering that the sightings that night were not made by one frightened civilian. They were made by a dozen or so military men, charged with the security of a nuclear base, who were SCARED. No one said "hey- I think that's just a lighthouse beam", or "that's just a searchlight".
You also ignore the corroboration by the civilians in the area, who saw nothing like a lighthouse beam, and who were familiar with conditions in the area.
I have a strange image of you being dragged aboard an alien spacecraft like that guy in the "To Serve Man" episode of "The Twilight Zone" screaming "But I thought it was just a lighthouse"! LOL!
Have to go. Keep watching the skies (just kidding)!