My take on that is that's not a complete Juubi.
Juubi can exist in BOTH chakra form (which is what you've shown) and vessel form (gedo mazou)
They are both not powerful in either of those state (inactive or downright rampaging) and needed to be combined.
That's why summoning the juubi, it is need to put all the chakra back into its body.
This juubi can be the same one but only the chakra.
When Kaguya was sealed, they returned the body back to Toneri and the chakra was once more split and now reside all over the continent.
If Naruto wants to, he can combine all of them and be a juubi jin (without the body)
The Juubi is probably the gedo mazou with extremely low chakra and that cage that he's in is the seal that the Hagoromo and Hamura Karma seals made.
Remember that Toneri became petrified and was effectively cut off from the world.
This could be what Urashiki had done.