In The Absolutely True Diary of a Part-Time Indian, how do the narrator’s steal and three-point basket affect the people in the gym?

To properly analyze the three-point basket and the reaction of the spectators afterwards, it's important to understand a little background. The Absolutely True Diary of a Part-Time Indian by Sherman Alexie tells the story of a Native American teen named Arnold Spirit, Jr (usually known as Junior), who attends an all-white school called Reardan High School. Eventually, he joins the basketball team and has to compete against the team from Wellpinit, the Indian reservation where he lives. The first time the two teams play, on reservation turf, Junior's old friend Rowdy elbows him in the head and knocks him out, and Wellpinit wins.
Reardan goes on to win every other game it plays, and Wellpinit also wins all its games and is undefeated, so the rematch, this time at Reardan, is highly anticipated. The incident the question refers to happens at the start of the game. Junior is guarding Rowdy, and when Rowdy goes for a basket, Junior steals the ball, races down the court, fakes out Rowdy, and sinks a three-point shot.
The people in the gym react with pandemonium. As Junior, the narrator, says, "The gym exploded! People wept." Junior's dad hugs and kisses the white man next to him. Junior's mom faints. People get up and start hugging and dancing and singing, and the band even strikes up a tune. The Reardan coach jumps up and down, and Junior's teammates scream his name.
The team from Wellpinit is unable to recover from this initial shock, and Reardan wins the game by a wide margin.
It's important to note, though, that at the end of the game Junior, instead of being ecstatic, feels a great sense of loss. He abruptly realizes that his team has humiliated the Indians from his home reservation and that these players live in much more difficult conditions than Reardan's players can even imagine. Junior feels so ashamed that he rushes into the locker room, vomits, and then bursts into tears.