Kringle said so and if you can not trust Father Christmas who can you trust?
There are places Anduriel cannot reach—your friend Carpenter’s home, for example, or your island, now that you have awakened it.
He also must pay attention. He can not spend all his time watching Harry if he has other things to do and other people to watch.
He is a fricking angel, or at least a fallen one... Harry is priority one with his host, Nic.. You can bet that Nic has a good idea that Harry got the goodies that he wants.
“No,” Kringle said. “That’s why Mab remains here, to secure this conversation against Anduriel. But you must exercise extreme discretion for the duration of this scenario. There are places Anduriel cannot reach—your friend Carpenter’s home, for example, or your island, now that you have awakened it. And the Fallen must know to pay attention to a given shadow, or else it’s all just a haze of background noise—but you can safely assume that Anduriel will be listening very carefully to your shadow during this entire operation. Anything you say, Nicodemus will know. Even writing something down could be compromised.”
Anduriel can’t look into Hades vault either, it was Nicky who surmised Harry had scooped the pool on superweapons, not Anduriel.
Then Granny Winter is suddenly mobile again. That certainly couldn't go bad for anyone. Whoever would think that?!