Continuity mistake: When Dr. Loomis is thrown through the window by Michael Myers in the school notice that Myers' hair has strangely turned white. The next scene Myers' hair has gone back to being brown. This is more evident in the widescreen version. This is because during the hectic shoot, an unfinished mask that wasn't painted or dyed yet was accidentally grabbed by a crew member for that one shot. It wasn't caught until the film was being edited. (01:13:50)
Visible crew/equipment: When Dr. Loomis arrives to the gas station the boom mic's shadow is visible on the ground. (00:19:02)
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.