Look at the appendix, they report three different "scopes" for emissions. yeah, they could move anything polluting to somewhere else in the alphabet umbrella, but it's still in-scope for reporting.
"Scope 1 emissions are direct emissions from sources we own or control, such as company vehicles or generators at Google’s offices and data centers. Scope 2
emissions are indirect emissions from the production of electricity we purchase to run our operations. The location-based category reflects the average carbon intensity
of the grids where our operations are located and thus where our energy consumption occurs. The market-based category incorporates our procurement choices, i.e.,
our renewable energy purchases via contractual mechanisms like PPAs. Scope 3 emissions are indirect emissions from other sources in our value chain, such as
business travel or our suppliers"
By the way, the scopes are all part of the standard WRI greenhouse gas protocol for reporting emissions. You might be interested in how the market-based method works.
I don't see how Nest Labs would be considered to be part of Google the company, or in Google's value chain. They're just part of the parent company, Alphabet.
"Scope 1 emissions are direct emissions from sources we own or control, such as company vehicles or generators at Google’s offices and data centers. Scope 2 emissions are indirect emissions from the production of electricity we purchase to run our operations. The location-based category reflects the average carbon intensity of the grids where our operations are located and thus where our energy consumption occurs. The market-based category incorporates our procurement choices, i.e., our renewable energy purchases via contractual mechanisms like PPAs. Scope 3 emissions are indirect emissions from other sources in our value chain, such as business travel or our suppliers"