None of this really matters - it's just really "fun fact" semantic territory that doesn't have much deeper meaning. Whether "capitalism" as a word was coined by socialists and backdated all the way to Smith, the theories and workings of the modern "capitalist" economies exist for appraisal independent of the word's etymology. (Also, one might note that numerous criticisms of capitalism from socialists are accurate.) Then, capitalism is necessarily a broad church; it is subdivided into more descriptive categories to represent different flavours of the same basic economic principles - much like any similar construct common in economic, politics, philosophy, etc.
Nor have modern criticisms of capitalism much to do with Stalinists, because there barely are any Stalinists. Capitalism is becoming a dirtier word because of the huge widening of the wealth cap since the 1980s, slowed wage growth for the poorer elements of society (or even slower growth generally across society) and related problems like unaffordable housing, because more and more people cease to see the socioecononic and political system as working for them. You could contrast today with the capitalist postwar heyday to the 1970s, where it was providing huge increases in wealth and human development across rich and poor alike.
Where you have the most logic is that people are not necessarily objecting to capitalism. If people see that they appear to be the losers in societal economic distribution, hostility grows to the system generally. As the system is fundamentally capitalist, "capitalism" suffers by association, even if people aren't truly objecting to capitalism's core principles. As someone or other said of Keynes: he came not to destroy capitalism but to save it, and that was by seeing that it delivered clear benefits across all of society. But that's not a filthy socialist ("Stalinist") trick, it's just the human cognitive habit to tend to transfer feelings about things to other things by assocation.