In this case it's not "falsely". As was said of Trump, he doesn't use a dog whistle, he uses a regular whistle. He promotes racist stereotypes to drum up fear. He flouts standards put in place to protect people and democracy. According to his administration, in an effort to dismantle environmental protection in favour of industry, a little radiation is good for you. He tells people down is up in defiance of their own senses.
Anyway, the negative connotation of populism comes from mob mentality and appeal to baser emotions. Populism at its worst tries to convince everyone that the people who actually have the greater good at heart are the enemy and the ones taking advantage of you are your saviours. Scientists, for example, who try to dedicate themselves to bettering the world are supposedly the elite, and somehow driven by a self-serving agenda while those who are actually raking in the cash at your expense escape their notice and critique.