Signing up for Fiber requires creating a Google account, and the way the policy is written, they can share non-personally identifiable information about your online activity with advertisers so long as they don't tie it to your Google account. Between those two clauses, and pervasive use of Search/Gmail/Analytics, there's probably little activity they can't pick up.

Also, note that they explicitly say they'll tie your TV-viewing habits to your Google account. It's easy to overlook this, but TV ad revenue is still 50% higher than online ad revenue, so this is a major synergy.

Not associated with your Google Account doesn't mean isn't tracked, kept, or otherwise used.

It references their general Google privacy policy to show how they use information about you. The same privacy policy that allows them to stalk you across the world.

Also even if they didn't, Google has a monopoly over search engines, so this just vertical integration. It would be like Microsoft saying "we don't spy on OneDrive, but Google spies on Google Drive!" while microsoft then spies using Windows it knows that 95% of users will have installed. Distinction without a difference IMO.