They sang songs with lyrics about New York together and that was that.
Other, less-likely factors:
New York loves Mamdani. Trump loves New York.
Trump wants to align himself with winners, and Mamdani is a winner.
Mamdani explained to him how doing what is good for New Yorkers would result in a boom for businesses and the economy.
He feels comradery over the ragebait questions from the press.
The writing is on the wall with a low approval rating and the Epstein Files. He sees his loss of support and party circling like hyenas. He's desperate and/or willing to try something different to save face. Maybe he becomes a Democrat. He never admitted to supporting Project 2025 and friends, and would betray them to serve himself. He doesn't give a shit as long as he stays in power. Woke Trump 2026.
Hell yeah. And Bergtatt, "ahh, just right".