Dunno. That's sure what it looked like, though, didn't it? All we know for sure is that Mor Dhona is where the aetherial rivers converge, and that Midgardsormr guarded a seal on that aether, and when he died, we saw a whole bunch of primals flying out of it. We've never been told what that was. It looked like primals were sealed there, but then what sealed them? The Allag? Why there? In what? We can speculate, but we have no confirmation. For all we know, it was a visual representation of "Oh, hey, lots of aether, and now primals can be summoned." On the other hand, Odin was sealed in a crystal in a spring. Maybe the other primals were sealed in the most crystalline region of the realm beneath a giant lake. Maybe we'll find out in 2.5!
