Why is the glum-faced man's (the marshal's) request for a drink and a smoke perfectly timed to easton?

when the marshal and easton depart together, they converse and become friends.

the marshal requests the drink in order to keep easton from revealing the embarrassing truth to miss fairchild.

the request for the drink gives easton the chance to try to escape.

when easton is kind in letting the marshal have a drink, the marshal decides to assist easton in turn.