Answer to Question 1
It is a specialization within anthropological linguistics that focuses on speech performance. An example would be a study of political speech or how profanity is used.
Answer to Question 2
They consider White people to speak in insincerities. Instead of seeing requests about someone's physical state as being social niceties and friendliness, they interpret this to mean that the person has little concern at all about the person with whom he is speaking.