Let me help: here's a passage from the paper itself "On one hand, some scholars argue that populism is inherently illiberal [...]. Populist movements embrace majoritarian politics and seek to suppress opposition, often through a charismatic strongman who pledges to dismantle institutional constraints in the name of executing the people’s will. Under this interpretation, populism becomes synonymous with authoritarianism."
So while you clearly don't perceive populism as anti-democratic ... because you're immune to "doublethink", or something — others, including some of the people actually cited in the paper clearly do. Also, famously: https://www.cambridge.org/core/journals/think/article/abs/po...
And oh BTW, no. The majority choice is not automatically a priori democratic, unless by "democratic" you mean the literal Greek etymology of the word and not its actual meaning: https://en.wikipedia.org/wiki/Liberal_democracy