I understand your point. But I have to point out that by "born" it means "they are brought to this world".

The tribes do not create Primals, they bring them to this world. And from what I have seen, despite still being stuck at level 20, the Paragons assigned a Primal to a tribe.

Speaking of which, we can get a better hold of this mystery, if we better understand the relationships between the Primals, the Paragons and the beast tribes. Does the main story shed some light on this after level 20?