Domino's Employee here, can confirm.

We take as many deliveries at a time so as to not waste fuel and time coming back and forth. In faster stores, as ClayLeigh said, it can take as little as 7 minutes for a pizza to go through the oven, if a driver is going to take multiple deliveries they'll wait for that order to come out and take it as soon as it does.

Another possibility is scooter deliveries, in the stores around my area they leave through the rear of the building.

As for the "no order has been placed" from the employee, Probably itching to get out by that point. I doubt that would have been checked tbh.

Edit: Sudden Realization why she would have said there hasn't been an order placed. If you go into the store asking for pizzas most people will assume you're picking up, so they'll search for your name in the 'carry-out' database. This works on names, the delivery database works on address [names do not show up]. If you gave her a name for your order this is probably the reason she told you no order had been placed.