Reading the text, it looks like the word "emphasize" was a delivery instruction written in the text they gave him to read.
Biden offers first remarks on airstrikes: We don’t ‘seek conflict with Iran’
03/24/23
https://thehill.com/homenews/administration/3917234-biden-offers-first-remarks-on-airstrikes-we-dont-seek-conflict-with-iran/
President Biden on Friday said that the United States does not seek conflict with Iran, while offering his first response about the airstrikes the U.S. conducted in Syria after an Iranian drone hit Americans.
“To make no mistake, the United States does not — does not, emphasize — seek conflict with Iran,” Biden said during a press conference with Canadian Prime Minister Justin Trudeau in Ottawa. “But be prepared for us to act forcefully to protect our people. That’s exactly what happened last night.”