Doesn't calling right-wingers "populists" do the very same?
There is a big qualitative (not just quantitative) difference between condemning a few manipulative politicians, and condemning, say, an entire ethnic group or rival political party.
It's true that Trump has mocked mainstream politicians, and this is probably equivalent to non-populists condemning populist politicians. I suppose one could argue that a critic of populist politicians is hypocritical if they also condemn Trump for mocking mainstream politicians, but I don't know of any examples of such criticism. (It might also be worth noting that this particular phrase was used by, among others, Nancy Pelosi in 2006).
As for the "deplorables" quote, I don't want to defend it; however, to substantiate my point about qualitative and quantitative differences, I have to mention that in the infamous sound bite she said that "half" of Trump's supporters could be placed in that basket, and then later regretted specifying "half". (In previous speeches she apparently made it clearer that these supporters were only a small fraction).
Politicians of any affiliation are prone to highlighting the extremists among their opponent's followers (likely due to the psychological biases of Group Attribution Error and Ultimate Attribution Error, or, more cynically, due to a desire to exploit those biases) as a way to tarnish people's opinion of that opponent. That is a problem no matter which politician is doing it, but I still think that the bigger problem is a politician targeting groups of people based on immutable characteristics like ethnicity (or institutions like the media).
With a bit of perspective it's easy to see that this broadly describes socialism - which is the parents point. Socialism and social democracy is not commonly derided as 'populist'.