Two things,
the Passport Cards are in backlog until probably mid September maybe later. After that, they should be produced normally as the passport is ...
Secondly, some people get the passport and Natz Cert in the same mail, if the passport was produced in the office that adjudicated the passport application. This happens when there in not a lot of passport production going on in that office.
Most passport applications are sent to a remote printing center (at another location different from where the application is approved), thats why you might get two mailings. One from the location that adjudicated the application with your Natz Cert and other docs and one from the remote printing locations that printed out the passport.