why does gene tell mr. prud'homme about the beach?

Gene reflects upon telling his teacher because it demonstrates the easy going atmosphere of the summer term. 

"Summer lazed on. No one paid any attention to us. One day I found myself describing to Mr. Prud’homme how Phineas and I had slept on the beach, and he seemed to be quite interested in it, in all the details, so much so that he missed the point; that we had flatly broken a basic rule. No one cared, no one exercised any real discipline over us; we were on our own."