Visible crew/equipment: When Loomis looks out the window for Michael, you can clearly see the cameraman's reflection (best seen on the Limited Edition DVD).
Visible crew/equipment: When Dr. Loomis arrives to the gas station the boom mic's shadow is visible on the ground. (00:19:02)
Visible crew/equipment: When the sheriff and the officer are talking after getting the gun from his car, you can see a crew member in the background (doorway).
Answer: It's never explained who told Jamie of her murderous uncle, but Jamie is mocked and made fun of by her classmates for being related to the infamous Michael Myers. She could have been told by her adoptive family, classmates, neighbors, etc, but the movie never provides any definitive answers.