Apple knows nothing about your cards (they are all encrypted on-device), and nothing about your transaction except that there was A transaction (since Apple just sees a token that gets passed from you to the card provider).
The merchant doesn't see your real cc number, just a one-use token. So they can't track you unless you choose to add a loyalty card.
The card provider sees all details of the transaction. Just as now, and what you want.
And the real cc details are stored in dedicated silicon on a fingerprint-locked device.
It's worth noting that the token is one-per-vendor, rather than one-per-payment. This is what allows TFL to match your tap-in to your tap-out on the London Underground, and what allows them to apply daily/weekly capping on fares.
The article highlights CurrentC's brazen lack of privacy. From their policy:
> We share your information across our network of merchants and with our third party service providers. MCX may share...To third-party analytic providers and advertising partners to help us deliver, track and analyze the operations and effectiveness of our marketing campaigns, promotions or advertisements.