Nobody decided, or kinda we all decided on aggregate, I guess. It's normal cultural development of a community. Hexbear is a bit like an island, sheltered from the most extreme currents of the interwinds but always in dialogue with them. Sometimes a new term gets carried here, and sometimes that term has more staying-power here than elsewhere, so it sticks. It might also shift in meaning, relative to more common definitions. Bazinga brain could be a hexbear original, but I'm not sure, really.