BTW, missile shots from Vandenberg are very common, often aimed at Kwajelein Atoll in the south Pacific. Radars on Hawaii and Johnston Island are usually used to track them, plus radars on ships based in Hawaii and Midway.
This one was from the ocean, or possibly one of the Channel Islands. A shot from a sub is not unlikely, and quite possibly a test of a United States SLBM also aimed at Kwajelein. Wouldn't it be reasonable to shoot it from the same vicinity as the land shots, so they could use all that nice tracking equipment?
And, might it make sense that they wanted it to land in daylight so they could use optical tracking, or maybe even the Mark I Eyeball? Then it would have to be launched in mid to late afternoon... as this one was.
And... all those who believe the military
never has a good reason to keep various launch information secret, please raise your hand......