The casually dressed are rarer in this section, and tend to be getting discreetly disapproving eyes. River's boots apparently pass muster, though, or at least can be overlooked because of the gown above them; nobody looks at them twice as Duo maneuvers towards an empty table.

It's probably to the good that he's steering, and that River still has her hand on his arm, because she's giving most of her attention to the ceiling. (Possibly looking for clouds.)