It’s ambiguous at best.
They wont (or cant) prove they hold the bitcoin.
Fact is they dont need to own it. They only need to own it when a customer sells it.
This allows them to game the system.
Are they?
They say they’re not.
If that’s good enough for you, okay but its not remotely believable to me.
I come from this business and if you provide an incentive to cheat, they will.