Why is Johhny willing to tell Rab the story of his accident when he was unwilling to tell others?

Rab seems to be intuitively aware of the problems that trouble Johnny. He offers Johnny food in a way that does not seem "scornful," so Johnny is willing to accept the food. Rab is quiet and almost insightful so that Johnny is ready to share his story and his troubles. Even when the story is told, Rab offers Johnny a job which Johnny initially refuses. Yet Rab is accepting and is willing to offer Johnny the job at a later time if Johnny cannot find other employment.