Honestly I’m not technically knowledgeable enough to answer, you can have a read of their FAQs. But my understanding is that the sandbox allows some google services to be used, but without privileged access to the rest of the system. As opposed to blocking them entirely, which would mean you couldn’t use those services at all. https://grapheneos.org/usage#sandboxed-google-play
I wonder if there is some benefit from the clients interpretation of the reading, even though the reading itself is nonsense. In the same way someone can flip a coin to help you make a decision, and you realise from your gut reaction what you actually wanted to do all along, but weren’t consciously aware of