I don't believe this is true. In incognito mode you don't have the same gaia or dblck cookie ids. Your traffic is logged in icognito mode by Google but as a different user under a different identifier.

Now certain websites could use tracking methodologies based on ip address and device signatures to identify you as the same user and set a cookie identifying you as the same user for purposes like remarketing, but Google itself doesn't join this data from their own logs.

This announcement is just clarifying that Google does log data in icognito mode as do other websites. It doesn't say that Google joins your icognito session data with your non-icognito session data.