I do think that whether or not his father is invited to or told about his funeral does depend on the relationship that they had with each other. That being said, I can understand that now that his son is gone, there is a lot of grief (afterall, now it's final. There will never be reconciliation), and attending a funeral (which is for the living I believe) brings closure for some. I can see why he thought he would go, even if I can understand why Cory's mom wouldn't have invited him.
Also, the article said "no one got back to me", which makes it sound like he did try to find out the details of the funeral.