When a speaker starts saying thank you to the audience like that, and this is with any speaker. They are telling the audience , that is enough, thank you, now please stop so I can begin speaking.
He is saying, that is enough, please be quiet.
Instead of saying shut the fuck up.
THis is one of the reasons President Trump started speaking to us, with no holds barred. Politicians have their slimey way of being so polite while stabbing us in the back. Trump pulled that curtain away and then all sorts of trash started spewing from their mouths.