Author here. The API testing tools I used before mostly focused on making writing tests easier through a nice GUI. I would rather have someone else write the tests for me, thus this experiment. Please voice your opinions, and try it if possible. Much appreciated!
Good questions. The main difficulty IMHO is that it's hard to know people's intentions. We can't just parse the target program and generate tests, because then the tests will always pass. I picked API testing because people have a Swagger spec already, and it documents how the API should behave.