There's an alleged oral explanation of who "really" owns the diamonds at issue that allegedly "enlightens" what's actually written on the piece of paper (i.e., contract) with Sotheby's. The Court of Appeal holds that this alleged oral explanation means that the case can go forward, since the contract is ambiguous.
Okay. I see the argument.
But there are still two owners listed on the document, Sotheby's (allegedly) released the diamonds to one of the two listed owners, and Section 1828 of the Civil Code says you're allowed to do that without any liability attaching. So unless there really was an oral modification that "explains" the "true" ownership, Sotheby's is off the hook.
But that's for summary judgment, or (more likely) trial.
Then we get to figure out the details of what really happened.