How did Hundert develop or change?

As Mr. Hundert steps onto the ladder of the helicopter to leave the island after the contest, Sedgewick Bell remarks that he has not changed. Each of them behaved exactly as they did when Sedgewick was a boy and Hundert a young teacher at St. Benedict's. Hundert reflects on this and, coming to the conclusion that Sedgewick was right, takes it upon himself to attempt one last encounter. When Sedgewick is addressing a meeting of miners and presenting himself as a champion of the working man, Hundert joins the audience, and Sedgewick point him out as his old history teacher from Richmond Central High School. Hundert refuses to take part in this deception and tells everyone that Sedgewick was actually his pupil at St. Benedict's, an elite private preparatory school.
Hundert reflects that his words made no difference at all. However, he has the satisfaction of knowing that he has finally spoken out against Sedgewick and attempted to expose his lies. In the end, the reflection that he had not changed in forty-four years forced him to change in the forty-fifth. He realizes that it is never too late to develop the integrity and character he has preached for so long.

Hundert did not register a substantive development in the story. He was portrayed as a coward and a cheat during his days as a teacher at St. Benedict’s. Hundert had developed a soft spot for Sedgewick Bell, a student in his class and son to Senator Sedgewick Hyram Bell. Hundert had given the younger Sedgewick an A instead of a B in one of his quizzes, thus inappropriately helping him to secure a spot at the “Julius Caesar” competition which was held at St. Benedict’s every year. Additionally, during the competition, he realized that Sedgewick was cheating but did not take any disciplinary action against him. Instead, the issue was forgotten after he bowed to pressure from Senator Hyram Bell, Sedgewick’s father, and Mr. Woodbridge, the principal. Thirty nine years later, in an island far from St. Benedict’s, the same competition was replayed, and Sedgewick Bell was among the competitors. Once again, Mr. Hundert realizes that Mr Sedgewick was using a transmitter in his ear to get answers to the questions that were being asked during the competition. However, instead of having him disqualified for the irregularity, he chooses to proceed with the interview. This shows continued cowardice and his neglect of the moral obligation to tell the truth despite the two events being years apart.
https://www.westmorelandschool.org/cms/lib/NY01914042/Centricity/Domain/125/thepalacethief.pdf

I would argue that Hundert hasn't really changed at all. The fundamentally static nature of his character is cruelly exposed when the loathsome, entitled Sedgwick Bell stages a rematch of the Roman history contest at which he'd cheated—but still lost—all those years ago at school. In the intervening years, Hundert has still not developed the necessary moral courage to call out Bell for his cheating. The history quiz rematch would've been an ideal opportunity for Hundert to show the whole world just what kind of a man his former student really is. But Hundert's too much of a coward to do the right thing, just as he was when he was Bell's teacher. Then as now, Hundert desperately wants to conduct himself with integrity and honor, yet buckles spinelessly under the weight of pressure and intimidation.