I guess it was written by an English teacher and the story was a conversation between her and her colleague. Her colleague couldn’t sleep well the day before. The reason why this person - I think this person was male so I will use “he” instead from now on – couldn’t sleep was he didn’t have a confident of teaching English. He was afraid that his students started asking difficult grammar questions which he couldn’t answer someday. For example, what is the difference between “a” and “the”? It seemed He didn’t have a right answer. I found it really interesting that he had a sense of guilt. I’ve never expected this.
Usually it is written that they want a native speaker but a person who has a degree of teaching English. I met a teacher who didn’t have a degree. Mind you, I know many teachers who have a degree and keep brushing up their teaching skills!
In my opinion, it depends on the situation. Most of Japanese want to speak English but not seriously. Students want to speak or have a confident in speaking English. There is no life threat if you can’t speak English. Then, the teachers don’t have to have a degree. They require good personality and patience.
If a person who will go abroad for his business and must have English skill in one month, he wants a teacher who has a degree.
Anyway, students must consider carefully what kind of class they want to take.