The exposition is for the audience, who have no idea what Mos Eisley is (in 1977 when the film was made and was a self contained thing).
I never thought seeing the movie at 11 that Luke was some indentured servant on the farm, he talked about going to Tosche Station (on his own) so clearly he has reign to come and go.
I meant that the only place he could go alone was Anchorhead and Tosche Station. I’m sure he’s heard stories about Mos Eisley, but was never allowed to go there alone.
Most of the stormtroopers were there in Mos Eisley.