What did the writer feel about his own and his friend's behaviour when Herr Boschen sang? Is there any lesson for all of us in it?

They felt rather sheepish when they discovered that Herr Boschen's song was not meant to be funny. I suppose the lesson might be to reserve one's judgment about what people say and their motives for saying it. They should not have laughed at the man simply because the other young men told them the song was a comedy.