Why do so many anti-nationalists use the term populism as if it's synonymous with nationalism? It isn't.
The particular anti-nationalists do it because they don't want globalist populism to overtake globalist crony-corporatism. They want plutocracy, not rule of, by, and for the whole People. They want wage and salary slavery so their masters can have the largest slices of the pie regardless of whether it harms increasing the pie and does vastly more harm than it benefits anyone.
Populism simply means for the whole People rather than for those who want to lord it over the rest.
There is right-wing populism. There is left-wing populism. There is populism in one state. There is global populism.
I happen to be a populist. I am also an economic left-wing radical. I am also a democrat. I am also a one-worlder (a globalist). What I am not is an anarchist. I'm for good government, not against government, not against the "state." For me, the proper state is the People democratically deciding the economy through as little representation as possible but rather through as much direct, pure democracy as practicable.