You can easily validate this by checking all the "pixels" (in the RTB sense) that are being deployed by Google. In their defense, they do mask a lot of things so stuff like the full IP address are not available (last time I worked on that they just give you the three first segments) but still quite a few information was available to target your demographic segment.

Edit:

For downvoters and people curious about tracking pixels: - https://support.google.com/dfp_premium/answer/1347585?hl=en - https://support.google.com/dfp_premium/answer/2508388?hl=en