Weird. I think you might be jumping to conclusions though. On the odds, it's much more likely to be some stupid prank call, even from people not at your school than your stalker from WP.
I could be wrong here, but I think it is unusual for stalkers to 'stop and start' harrassing the same victim. If they had access to your number, they probably would have called you long ago (depends how far in the past the stalking happened of course).
In my high school, there was a fad for prank calls for a while. Not everybody did it, but if only a few did out of every school in the country for a couple of times each... that's quite a lot of phoney calls going around and you're just as likely to get one as anyone else.
My advice would be not to stress at all about it. Don't expect it to happen again. If it does, just block the number or even change yours and go unlisted.