Is the appetizer of a three-course meal always a salad?
The three sentences you quote are example usage of the phrase, and not part of the definition. These are simply sentences that demonstrate usage of the defined phrase, but are not part of the definition.

The definition, which is always true, is this part:


  A three-course meal is a meal that consists of three parts served one after the other.


Other statements that could be true of a three-course meal:


A three-course meal can cost significantly more than $10.
The three-course meal could include courses of a salami, a pasta, and a meat.
The last course of a three-course meal could be a salad