I agree they aren’t contradictory. But they aren’t the same thing.
What is certainly true is that fascists often adopt the guise and language of populists as a means of currying favor with a gullible public. Fascists are manipulative and deceitful. Less often are they clowns like our current wannabe dictator President-elect.
Populism isn’t necessarily authoritarian and nationalistic. Fascism is extremely authoritarian and nationalistic.