This is a major nitpick, but who the *beep* buried Jason in the cemetery? It's not his unmarked grave from when he was assumed to be dead as a child because, well why would he be there. Secondly, his mother is dead and no other family has been mentioned. Tommy Jarvis and the Jarvis family buried him then? The city? Who?
shareThere was a subplot involving Jason's father, Elias Voorhees. He is the one who buried Jason. This didn't make the final cut of the movie but it was in the original screenplay.
shareThis is in the trivia section for the movie here on IMDB:
"The original script contained material that alluded to Jason's father, which, to date, remains the closest the series has ever come to shedding some light on the mysterious character. In the script, Pamela's headstone is next to Jason's, a reference to the fact that someone paid to have Jason buried, explaining why he was not cremated as the Mayor said in Friday the 13th: A New Beginning (1985). As well as this, there is a final scene in which Jason's father visits his son's grave, seemingly aware of the fact that Jason is not inside it. These scenes were never filmed, but made it into the film's novelization. The 2009 Deluxe Edition DVD uses storyboard art and voiceover work to complete the scene."