It was my understanding that the chrome browser "phones home" all the time, but maybe i was mistaken because I can't find a reference. I did find this from wired:
Other steps Google must take will include continuing to “block third-party cookies within Incognito mode for five years,” partially redacting IP addresses to prevent re-identification of anonymized user data, and removing certain header information that can currently be used to identify users with Incognito mode active. ¹
So it looks like chrome was configured to pass along identifiable header information?