Continuity mistake: Before taking Michael's mask, Corey calls Allyson and tells her to meet him at the diner at 9:00 pm. Later we see Allyson at the diner waiting for Corey, but when she checks her phone and sees Laurie is calling the time is 5:36 pm. (01:13:56 - 01:24:41)
Continuity mistake: In the beginning credits Lindsays name is spelled Lindsey. In the ending credits its spelled Lindsay, the correct way.
Continuity mistake: When Corey is almost hit by a car in the beginning (after the credits roll), his bike is suddenly toppled much further over after the camera cuts to a wideshot.
Answer: The implication seems to be that there is some sort of subliminal connection between the two that they both pick up on. I personally took it as Michael somehow subconsciously feeling the "evil" brewing within Corey... almost as though he sees his own evil in Corey. Thus, he lets him go and subsequently "teams up" with him later on. They're a twisted form of kindred spirits.
TedStixon