'Incognito' implies anonymity. The clear
suggestion is that people who already know who you are (your ISP, or your employer/school who is equivalently knowledgeable) can see your browsing, but that websites will see you as an anonymous person unless you choose to identify yourself to them.
There's a reason Google don't mention their own collection/inferential behavior here; people might abandon Chrome is it said 'BTW if we can work out who you are at the server end we'll still be tracking that.'
It may boil down to determinations of what 'a reasonable person' believes, that is someone who is amenable to reasoned argument, and of ordinary knowledge. I think a lot of people here are projecting their technical knowledge into this page and saying 'if you don't consider all these background factors then that's your problem.' It seems like to me that a court will lean towards taking the above at face value absent specific knowledge to the contrary, eg choosing to log into an online service vs not.
A simple example would be doing some Super Secret Stuff in one incognito window and opening up another tab where you go to Youtube (also incognito), don't log in, but play your three favorite and quite unusual songs for background music. Is it OK for Youtube to silently infer that it's you based on that highly individual selection and allow Google to track your Super Secret activity with 99.9% confidence?