Willy has a secret that he seems to have kept from himself for a very long time. Or at least it's a secret that he hasn't taken out and looked at very often in the years since he kicked Biff out of the house. Willy was having an affair with a woman up in Boston, and Biff discovered it when he went to the hotel to get his father to help him with his math teacher who had flunked him. This discovery was a singular turning point in the relationship between Willy and Biff and a major turning point in Biff's life as well.
The two women Happy arranges for in Frank's Chop House that last night of Willy's life are a foreshadowing and a deadly trigger for Willy's memory of that night long ago (but oh, so present) in Boston.
And what values of Willy's does Happy exhibit in the restaurant? Happy, like Willy, is a salesman, and he snows the first woman into believing that he sells Champagne and that his brother Biff is a big football star. He's con man, a joker, and a womanizer just like his old man. Nothing serious, I suppose, but more than serious enough for that particular evening.
And don't forget, Biff runs out of the restaurant, and Happy, along with the two women, follows him, leaving Willy, with his past and his regrets, alone on the bathroom floor. Happy, who Willy always favored less than Biff, pays his father back with his own thoughtless disregard.
Willy is in his state of constant disillusionment and even in the restaurant begins to break down. Happy in the end just tells the ladies that he does not know his father and leaves. Once Willy starts going crazy the boys end up leaving him. Happy takes on the role of a salesman similar to his father. He ends up faking that his brother is a huge football star and pays for the champagne in order for the girls to be impressed. Both Willy and Happy show disillusionment while one is on purpose and one is by helplessness.
I would also like to mention that it helps add to the chaos of the scene. Willy is already suffering from the constant flashbacks, his descent into insanity, and he has just been told by Biff that he was unable to meet with Bill Oliver. He is remembering what Bernard told him, and he is also beginning to remember his trifles with the women. The chaos with the girls trigger the memory that we have all been waiting for. It helps build up the intensity that leads to the climax of the play, and then the bitter, alone aftermath that Willy suffers alone.