Uh, it's not a direct sequel to the 2nd one... It happens chronologically last, although yes, it does have flashbacks to the "car accident" from the ending of the 2nd movie, much like the 5th movie.
It's "Part 2" because it's dealing with the same thing that "Part 1" is, namely - the murders occuring all over the town. The murderer from the 2nd movie is revealed in the 7th one - if you didn't figure out who it was yet for some reason even though he was shown numerous times...
And it's long because it has a lot to cover. Also, as I said before, the theatrical run was ~15 minutes shorter than the announced DVD time so they might be including the epilogue on DVD (but treat it as a rumour since there's no confirmation on this).