This is not what he said.
You need 20 people up front to obtain the default (minimum) "Tribe" territory radius. You cannot grow into it from a "Clan". A "Clan" will be capped at 25 person territory radius. But can grow, member wise, as large as the "Clan" wanted.
The more I think about it, the more it makes sense. It's a good balance. I think this will work (especially when you implement tribal warfare and totem/territory takeover).
Jordi just did a not so good job in explaining it. hehe