It seems that people were not just expecting privacy but anonymity based on the fact that Protonmail does not generally keep IP addresses.

That seems to be an unrealistic expectation. General anonymity is not something you can just buy. It only lasts for a limited time and takes considerable work on the part of the user. It was obvious to me when I encountered the claim in question that it was about preventing the commercial exploitation of personal data and not some fundamental discovery that changed the normal exceptions of what was achievable in terms of anonymity.