I just made a CA Grill reservation this past weekend for our anniversary in August and on my confirmation it says:
Due to capacity constraints as well as the numerous private functions hosted by the California Grill, only patrons of the California Grill may use the 15th floor observation deck at Disney's Contemporary Resort.
Guests who have dined prior in the evening may return to California Grill to view the fireworks. Guests will need to present their receipt from dinner to gain re-entry to the restaurant.
As an alternative, Disney Resort Guests who are visiting Disney's Contemporary Resort for shopping or dining experiences may visit a fireworks viewing location on the north end of the 4th floor Grand Canyon Concourse. Proceed past the Concourse Sundries and Spirits shop and exit the doors to the exterior. From the viewing area, Guests can see Cinderella Castle and Magic Kingdom® theme park, and hear the background music and sounds synchronized with the Wishes fireworks display. There is a small area under cover for viewing during inclement weather.
The sushi and Chef's counter are seated on a first-come, first-served basis.
While you do have to have either a reservation or a receipt from dining earlier the same day, it seems the sushi bar area (in front of the chefs) is seated on a "first-come, first-served basis." To me, this would imply that you don't actually have to have a reservation to be seated there, however, it's not really clear and I've never personally eaten at CA Grill w/o a reservation (and why would this appear on the reservation confirmation?). Certainly, a reservation would guarantee your admittance. Perhaps it means that you can request to eat at the bar when you check-in at the podium, but you're seated there on a F-C, F-S basis
I would call WDW-DINE to find out or maybe someone will post who has eaten at the bar-area w/o a reservation.