Technically speaking, if they’re on the same WiFi subnet, there’s no reason why a Nest can’t talk to sensors directly without using the Google mothership as an intermediary. It could even auto-discover occupancy sensors on the subnet.
And the self-programming firmware is internal to the Nest. Again, no intermediary needed to spy on users.
As far as sharing, I was the kid who hoarded all the toys in kindergarten 🙂
