Why is Elie shocked because of something Rabbi EliaHou's son had done?

Eliezer tells the Rabbi that he hasn't seen the man's son, but after he leaves, he realizes that he actually had. The son had seen his father falling behind in the pack, but he had continued to run farther and farther away from him. He had been trying to get away from the burden of looking after a weak father. Eliezer prays to God for the strength never to act in the same way that Rabbi Eliahou's son did.

he tried to separate himself from his father.