That order was also walked out to the customers car.
The real issue for the waitress is the time spent on providing service for what was easily 5 or 6 tables of food was worth more than the $0 she got in tips.
SOME people seem to be ignorant or intentionally stupid about what duties go into the jobs of other people.
For whatever reasons, the industry has accepted and implemented a very low wage scale for servers of food in restaurants. The arguments over whether this is "fair" or "just" is not something most would wish to discuss. It simply is the norm. It is also a system enabled by the consumers, many of which bristle at tipping, simply because they feel the price paid for a meal is what they are required to pay. They know very well that servers are paid sub-minimum wages and they are happy to go along with the system.