Kamala Harris never became President of the United States. She served as the 49th vice president from January 20, 2021, to January 20, 2025, under President Joe Biden and then left office when Donald Trump, with JD Vance as vice president, took office after winning the 2024 election. (en.wikipedia.org)

In 2024, Biden did abandon his reelection bid and endorsed Harris, and she became the Democratic nominee. However, she lost the general election to Trump (312–226 in the Electoral College, 49.8%–48.3% in the popular vote), so the scenario "if Joe Biden doesn't run for a second term" did not result in her becoming president. (britannica.com)

Harris briefly served as acting president for about 85 minutes on November 19, 2021, while Biden underwent a colonoscopy, becoming the first woman to assume the powers and duties of the presidency under the 25th Amendment. (en.wikipedia.org) However, contemporary reporting and analysis explicitly note that this did not count as a woman serving as U.S. president; the United States is still regarded as never having had a female president. (abc.net.au)

Because Harris did not become president either by succession during Biden’s first term or by winning the election after Biden declined to run again, Jason’s prediction is judged wrong.