But he, on the other hand, a wit in his own class, a gay quizzer and laughter-maker at dances and Sunday picnics, had found the making of fun and the breaking of good- natured lances simple enough in this environment.

And on this evening success stood at his back, patting him on the shoulder and telling him that he was making good, so that he could afford to laugh and make laughter and remain unabashed.
Later, Ruth's anxiety found justification.

Martin and Professor Caldwell had got together in a conspicuous corner, and though Martin no longer wove the air with his hands, to Ruth's critical eye he permitted his own eyes to flash and glitter too frequently, talked too rapidly and warmly, grew too intense, and allowed his aroused blood to redden his cheeks too much.

He lacked decorum and control, and was in decided contrast to the young professor of English with whom he talked.
But Martin was not concerned with appearances! He had been swift to note the other's trained mind and to appreciate his command of knowledge.
Furthermore, Professor Caldwell did not realize Martin's concept of the average English professor.

Martin wanted him to talk shop, and, though he seemed averse at first, succeeded in making him do it.