Why was Rudy selected for examination by the Nazi medical authorities? What was ironic about his selection?

In the Steiner household, Rudy and the younger children are setting up dominoes while their parents argue with the two Nazi agents in the kitchen about inducting Rudy into a special military school. Rudy eavesdrops on the conversation as the children set off the dominoes by candlelight. Rudy understands that by winning three gold medals at the Hitler Youth carnival, he proved himself not only to his former tormentor Franz Deutscher but to everyone. Rudy's parents refuse to let him go.

A nurse and a doctor have Rudy and two other boys remove their clothes for a physical examination at school. The nurse explains to a teacher in the room that they are creating a "new class of physically and mentally advanced Germans." The doctor says he will take two of them.