The comparison only works if the concept of a “hive mind” is as accepted and defined as the concept of a brain, which is quite literally what I was asking.

"Hive mind" conjures ideas of an omnipresent, all-controlling intelligence to me like startrek's borg, but I think this is more about the idea of a "superorganism" [0] like some bees and most ants where the group exhibits traits and "behavior" and "decisions" as a whole, beyond the ability of any single, specialized individual. Less superintelligence and more emergent behavior and complexity.

[0] https://en.m.wikipedia.org/wiki/Superorganism