Why did this person delete me from facebook?

I graduated from high school 2 years ago. There was kid in my class who I wasn't great friends with but we always spoke and talked in the classes we had together. I was always nice to them. I accidentally found out today that I has been deleted. A few months ago I decided to say hi to them since it had been awhile since I spoke to them. They deleted my whole Walpost and ignored me. He did seem odd tho, on his profile pic, he has a picture of vandersloot, the guy that murdered the girl from Aruba a few years back. I'm confused. I don't understand why I got deleted when we were always cool. I thought maybe it was my post on facebook but I only post once or everyother day and my post aren't even bad.