At the time he was saying to Gaza. He was saying to take Americans citizens who disagree with murdering innocent's, and put them in the place the innocent's are being murdered. As if that somehow would teach them something... All it would do is murder the Americans.
Edit: it was another one of those times he was showing how anti America he was
It's a classic dog whistle. He knows exactly what he's saying. He's just disguised it to appear so stupid that no one will hold him accountable for it.