In fairness, the fact that Luke’s father was a Jedi was kept secret.
Well, um, no. Ben was quite clear about that, actually.
Yeah I mean before Ben told him it was a secret.
JEDIT: Ah I get it you mean his reaction to learning that should have been different. Yeah maybe? But then how much does Luke really know about the Jedi anyway? If he doesn’t know what the force is is he really going to know Jedi rules and regulations?