If I was a Marxist-Leninist Maoist, and said anything as an answer, in my prediction, it would be that

"sure, Mao did support the Khmer Rouge, during the Vietnam War (understandably, due to the U.S make their forced error of bombing Cambodia), but he died before he heard the worst of its massacres, and Deng was the one who continued it to the end, even as the Khmer Rouge turned anti-communist and attacked Vietnam!"

and then some ML-Maoist anti-Deng drivel of Deng's foreign policy reflecting that of their market reforms