I don't really see the causal link here between "more close friends" and "growing polarization", and I'm having trouble finding the actual study - the link in the article seems broken.
I can't find more information on the actual distribution, but I think looking at the _average_ number of close friendships is a red flag. It's perfectly possible for some social groups to be growing, while others are shrinking.
It likely doesn't account for the evolving definition of what a "close" friend actually is.
Just because Jack and Jill know a bunch of details about each others' lives owing to facebook updates or group chats, that doesn't necessarily mean they share a strong connection, at least not in the traditional sense. But I suspect they might still feel a certain connection and belonging to each other.
It used to require frequent, active, quality communication to know someone well. Now it just requires a few clicks.
I can't find more information on the actual distribution, but I think looking at the _average_ number of close friendships is a red flag. It's perfectly possible for some social groups to be growing, while others are shrinking.