They were saying boo-urns.

Trump: I was in front of a large group of highly professional people, most of whom are from either other countries or the United Nations, people that aren't big into clapping, applauding, smiling, and I heard a little rustle as I said our country is now stronger than ever before. It is true. I mean it is true. I heard a little rustle, and I said, it is true. And I heard smiles. I said, I didn't know there would be—they weren't laughing at me, they were laughing with me. We had fun. That was not laughing at me. So the fake news said, people laughed at President Trump. They didn't laugh at me. People had a good time with me. We were doing it together. We had a good time. They respect what I've done. The United States is respected again.
Plenty more rambling here:

https://www.theatlantic.com/amp/article/571456/