Nobody truly owns any bitcoins..because the ownership is only established when you are able to apply a correct private key in a "send" tx (via hardware device or something else), albeit validation of the private key (at some other point in time) is possible. Before that, it is all allegedly. This is in principle, of course.
This is like saying that your house is not truly yours, until you put the key in the lock and open the door...
Eh...apples and oranges.
With a house, whoever legally holds the deed owns the house, regardless of who owns the keys.
With bitcoin, the private key
is the deed. As we have seen with CSW, a lawsuit can hardly prove otherwise.