As far as the crash, and the primals "Sleeping" under the lake. Remember the primals use aethritic energy to manifest them self's into the plain hydalin habits. I would imagen that the mor d'hona disaster was the largest expulsion of energy the game world has ever seen.
So lets put all the pieces together duct taped with the magical material known as "what if".
Lets say there were large enough releases in the past to let the primal's partly manifest them self's in the past. Beast tribes witness these individual manifestations, Religions are formed.
The disaster of mor dhona happens primals of all shapes and sizes use the energy to take stroll around the world reinforcing said religions.
The knowledge of how to summon the primals is brought to the beast tribes. And in a omg what have we done moment the summoned primal's brain wash and enslave them turning them into pawns of the primal war.
Its here that I want to point out something that I find very interesting. The two tribes that are for the most part are just chilled out, are the two that have no known link to a primal.
Where as the kobalts, ixal, amool, and sahagans (proxied by there reavers) will eat your face off rather then look at you.