This seems like a pretty odd thing to say unless the US has some kind of intelligence that the North Koreans are going to commit some kind of provocation during the Winter Olympics:
U.S. Ambassador to the United Nations Nikki Haley said in an interview with Fox News that her country’s participation in the 2018 PyeongChang Winter Olympics next February was an “open question” due to security concerns over North Korea, stirring worries in South Korea Friday that the Games could flop.
South Korea’s Blue House scrambled to rebut the idea, saying U.S. President Donald Trump had “promised” President Moon Jae-in during a recent phone call that his country would participate.
During an interview with Fox News’ “The Story with Martha MacCallum” on Wednesday, Haley said the U.S. government has not decided yet whether to participate in the games, adding, “What we will do is make sure we are taking every precaution possible to make sure” that American athletes are “safe and to know everything that’s going on around them.” [Joong Ang Ilbo]
You can read more at the link, but the North Koreans have not committed any provocation nearly as bad as what happened before the 1988 Olympics in Seoul when they bombed KAL Flight 858 killing 115 people. Despite that provocation the US still participated in the Seoul Olympics.