It is easy to put something in Trumps head as there is a lot of empty space in there.

http://shanghaiist.com/2017/04/20/trump_says_korea_part_of_china.php

As Trump is not known as an Asian history scholar, Kyung Moon Hwang, a University of South Carolina history professor, has charged Xi Jinping with putting a Chinese nationalist version of Chinese-Korean history into the US president's head. "Itís possible that Xi said something like this, as such a story has been part of the nationalist history project under the Chinese Communist Party for a couple of decades," Hwang told Quartz.

Though Hwang also conceded that Trump could have simply not understood the nuanced points that Xi was trying to make, or the history lesson could also just have been lost in translation.
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