That’s not what he said - the article even quotes him saying something else:

“There will be more than enough jobs for the citizens of your nation, especially those with vocational training. I do think these trends really do make it hard to imagine why we should have large-scale immigration unless you have a very specialized skill.”

He’s not saying that people won’t keep wanting to immigrate. He’s saying that the USA will have no (self-interested) reason to let them in.