How did actor tell his dialogue without seeing it?

Question

In the film shooting scene in Hail Caesar (2016) the actor enters and the director meets him:

here the scene starts:

Before any scene the actor reads the dialogue and peforms it. But here the actor directly acts for the shot. How come?

Answer 1

Because Hobie Doyle was totally unprepared for the shoot.

You have to remember two things:

1. Hobbie is not used to this kind of film at all. His usual movie is a "singing Western" - this is the first "prestige picture" he's ever been, and as such is not used to the shooting style, and doesn't know what is expected of him.
2. He had no idea he was going to be in the film. His appearance in this prestige picture is thanks to the studio wanting to broaden his appeal with audiences - if I remember correctly, he is sent straight from his meeting with Eddie Mannix onto the film set, meaning that he didn't have time to prepare regardless.

In short, Hobie Doyle had no time to prepare for this film, and his lack of knowledge of the type of movie he is now starring in may have meant that even if he did have the time, he wouldn't have been all that prepared.