I see three possible reasons:
1. The instructor tests your reaction to stress situation (hm, very peculiar test though)
2. The instructor just does not know how to correct your problems. It happens, in that case you just need another instructor.
3. The instructor is pretty old and he is aware of one more airman taking one more aviation job, which can lead to earlier retirement =)
Anyway, just keep going. Listen to all useful comments regardless of a person personality and attitude. Take the best stuff from even crappy critique. If that particular instructor cannot teach you anything, find another person. If the school is not suitable for you, find another one. It is your career and your life.