So, you have to learn 'Trump Speak' to understand that exchange.
'What do you say to people who are scared?' is a softball question saying: 'Please, here is a platform for you to assure the American people that things are going to be alright.' It is a dumb question, but also a free home run to answer.
Obama would go on and talk about the American way of life, what past generations have done in times of struggle (depression/stock market collapse/WWI/WW2), and what we need to do in the future. Everyone would feel better.
Trump sees everything as an attack. His response is to to make the question seem bad, so the idea behind is also bad. He doesn't believe people should be worried, but he cant articulate that. Instead, he attacks the narrative that people should be scared. 'Fake News' is sensationalized journalism, and anything that doesn't fit his narrative falls into that purview.
Once you figure out this cycle, you start to understand what his followers like. No non-sense, straight to the point, reality TV. Drama for the sake of drama.