The boys have broken a rule by missing dinner. How does Finny explain to Mr.prud'homme?

From the text:

We had been swimming in the river, Finny explained; then there had been a wrestling match, then there was that sunset that anybody would want to watch, then there’d been several friends we had to see on business—he rambled on, his voice soaring and plunging in its vibrant sound box, his eyes now and then widening to fire a flash of green across the room. Standing in the shadows, with the bright window behind him, he blazed with sunburned health. As Mr. Prud’homme looked at him and listened to the scatterbrained eloquence of his explanation, he could be seen rapidly losing his grip on sternness.