Burying a child is tragic.
But to answer your question, I would say most families have not suffered tragedy. Mine certainly hasn't.
If your psychologist asks you if you’ve ever thought about suicide: it is not being as in touch with humanity as you think to say; “Hasn’t everyone”.
Yes. This. And much more.
Here's what I think likely happened: your friend talked to other people who went through tragedy. He noticed something common in their behavior. It can be something so subtle that it's invisible to most people, but your friend notices these kind of things. Then when he talked to the current person, he found the similar pattern.
I imagine the author of this article is describing something along the lines of my friend's cognitive capabilities.
For example, I invited him to a BBQ at my friend's parent's house. (He was my roommate at the time, and had met my other friend a few times so this was not a random thing)
He talked to my friend's mother for maybe 15 minutes at the BBQ. She is a cheerful and loopy sort of person, and that was exactly the sort of conversation they had. On the drive home he asked me, "that family has been through a lot of tragedy, haven't they?". Indeed, it would break your heart to hear about them.