The author is complaining that non-educators are trying to tell him how to do his job, not that they are judging him and his fellow teachers based on the results: "Today I have listened to people who are not teachers, have never worked in a classroom, and have never taught a single student tell me how to teach."

There's a big difference between judging others based on the objectively observable results of their actions and ordering others to do things a certain way. If a non-programmer complains about slow or buggy software from a vendor, that's fair, but if he tries to tell the vendor how to write it, it's a completely different matter.