This part of the linked article made me laugh.

The Dunbar number is actually a series of them. The best known, a hundred and fifty, is the number of people we call casual friends—the people, say, you’d invite to a large party. (In reality, it’s a range: a hundred at the low end and two hundred for the more social of us.)

My Dunbar number is like two. Maybe three. Social I am not. It has been as high as seven or eight in my life, but that’s it.

How do people know so many people?