That's what I said, verbatim: "People's desire to belong to something is a thing, but the definition of that something is very fluid."
The instinct is there, but how that instinct manifests is absolutely a cultural construct determined by circumstances. There is no biological imperative that says I should belong to the group of people born less than 10km from me (or 100, or 1.000, or 100.000).
I think this desire to belong to a group is a very strong instinct, and it will be the strongest during our teenager years, up until we are 25 or so.
It is a biological imperative, not just a cultural construct.
Now, the size of the groups we are capable to create depends on our technology and culture, of course, but not the desire to belong to one.
Therefore, we have sports fans, anime and sci-fi subcultures, and so on.