Populism = populace, people, individuals.
Democracy = mob rule.
The two words are different but mean roughly the same thing. Populism has just been made into a dirty word over the years because it doesn't work in the same way democracy does.
Populism gives everyone what they want on an individual basis; whatever is popular to those people. Democracy is to take a vote and apply it across the board regardless of what some people want.
Example: My company mandated an office day once a fortnight. A small number of outgoing people love these days and think everyone else is a miserable git and anti-social. The people that can't get any high quality work done in such an environment, the 'anti-social miserable git' ones, have to just muddle through the day and try not to snap and staple anyone to their desk.
If the office days were on an individual basis, as in people were given the choice to go in, then staff morale would have gone through the roof, but the loud "I don't have an indoor voice" people in the company didn't want it to be done that way.