In my opinion, the staff at this restaurant did not seem to have very good management as well as lack of coordination. Maybe, since it was busy the staff may have felt under pressure, which may have caused them to mix up your order, or they may have been new staff, but they must be able to work under pressure regardless and organize themselves a bit more properly.
In my opinion I think the staff need to look after the customers and need to have good memory and good skill they shouldn’t make the customers wait long time. It’s also good that Milk complain because it’s will make the staff be more active and pay attention with the service.
One of the biggest reasons people don't come back to restaurants is long waiting and bad services. I think that restaurant manager need to look out their problem and train their staff more effectively with a better manage of each staff so they can known which part they need to take responsibility and make a better customer service to their guests.