It's completely different from H1 and 2. It has nothing to do with Michael Myers.
They tried to capitalize on the Halloween franchise but failed. It shouldn't have been included in the series.
https://en.wikipedia.org/wiki/Halloween_III:_Season_of_the_Witch
“After the film’s disappointing reception and box office performance, Michael Myers was brought back six years later”
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Took ‘em six years figure what went wrong. Oy.