When I see a politician or organization labeled as populist, it usually refers to the (quite common) practice of getting votes from dissatisfied masses by promising them impossible results, which they don't intend on even attempting to achieve.
Populism is not about ideology of regular people against the elites, that'd be apply more to e.g. various socialdemocratic parties who attempt such goals and ideologies but most of them aren't considered populistic especially if they're in power for years and have to actually implement policies instead of talking about vague results that'll magically arrive.
It refers to a tactic of identifying people who are dissatisfied with current reality and also with the realistic short-term prospects of how future is going to unfold for them even if the promises of the other parties arrive and reasonable economic growth and modest systemic improvement happens, and promising them unrealistic, unachievable improvement (often by suggesting major, radical changes that are a change but can't possibly give the effects they promise) - thus giving these voters hope that others don't, filling that (very valid) need and thus getting their votes.
Your definition is wrong. Populism is a political strategy based on the oversimplification of issues, inventing scapegoats, and generally appealing to popular "bar talk" as offering solutions to problems that are in reality way more complex. Other symptoms of it are an unwillingness to make compromises, not listening to experts, alluding to conspiration theories, an alleged fighting against the elites and for the "common man on the street" (as long as he's politically aligned), an US versus THEM mentality, anti-intellectualism, and discrediting media and science. All of this makes sense, because the populist needs to be able to sell his oversimplified solutions, and often science, statistics, and, generally speaking, the truth stands in the way. Most problems do not have simple solutions.
Populism is pretty much what used to be called "proto-fascism" by Ecco, but communists can also have a strong populist agenda. Where I live, in Portugal, the communist party used slogans like "Leave Nato, away with the Euro" in general elections - simple recipes that couldn't possibly have beneficial effects and that in reality nobody would implement.
What you define as populism has nothing to do with real-world populism, it's just a construct.
Part of populism is also claiming to be neither left or right on the political spectrum because it can be both or neither, a good example of this is Five Star Movement from Italy. But what is mostly common with populist movements is the appeal to the common man and blaming elites. So how the author of this article isn't advocating for populism is something someone needs to explain to me.
I don't necessarily disagree with that assessment, just wanted to correct your definition of populism by a more adequate one that is based on indicators of tendencies. There is no problem identifying right wing and left wing positions or discerning different brands of fascism, populism, socialism, etc. The people who claim that these positions cannot really be distinguished any longer are usually trying to push some sort of extremist agenda. A typical example are the recent "alt right" (= run off the mill Fascism, nothing special about it) attempts to promote the absurd and historically false claim that the German Nazis were left wing, because they choose the phrasing "national socialism". Of course, there are also similar attempts by populists to re-appropriate terms like "populism", that's not very surprising.