I agree. I mean jumping straight into a story full of zombies in some desert? Who would want to watch that? So i'm with you on that. The way the movie went, we got to see Dastan's world, other characters, etc, not just the duo tackling zombies.
I think that the scene is supposed to show that Dastan got it.
"The name "Dastan" translates to "the Trickster", a name Jordan Mechner originally found in the Shāhnāmé and which he found very appropriate for the character."
From wikipedia so take that as you will.