Guérin may not have known she was acquiring a style at the time of her training, but she was. Dancers at the School of American Ballet acquire the Balanchine style, and students at the Vaganova Academy acquire the Kirov style. It's simply a matter of how one is taught to dance. Likewise, the different companies of Paris Opéra Ballet, New York City Ballet, and the Kirov all have slightly different ways of executing the same steps and different styles of acting and temperament. Paris Opéra is more subdued than the Kirov, and NYCB is even more subdued than Paris Opéra, with regard to facial expression. I think that this is a result of nationality. Obviously, the country one is born in influences the way one acts, moves, etc. American dancers have a tendency to look mass-produced because just about everything in America is mass-produced. French dancers have a tendency to look "a bit offish," as the British say, and the Russians are just plain flamboyant (which comes in handy when dancing on a stage as large as that of the Maryinsky or the Bolshoi).
Now that I've finished repeating the article (not on purpose), I think it was an informative article for those who don't know ballet as well as others. I don't think Levene was disparaging the fact that there are different styles, only saying to the non-ballet-regular that they exist and that, when used properly, they are good, because nobody wants to see the same style everywhere, but when they are mixed together (think ABT), the results are not always harmonious.
Isn't there, in the "Links" section of this site, one that deals with different styles of ballet? I seem to recall one. I'll have to go look.
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CygneDanois