I think what happens here is that Orwell is having a big stab at the intelligencia, and the intelligencia at the time (as now) hated nationalism. He is trying

I think what happens here is that Orwell is having a big stab at the intelligencia, and the intelligencia at the time (as now) hated nationalism. He is trying to point out all the ways their behavior is just like that of overzealous nationalists at the time, so he redefines the word so as the label all the intelligencia as the thing they hate. It makes for effective rhetoric. I think anyone reading this should keep in mind that he seems to have good things to say about what he defines as "patriotism", which is what we would mean by the word nationalism today. In other words, he would absolutely not agree with the anti-nationalists of today who hate their country. In fact, he goes out of his way in this essay to label those people as prime examples of "nationalists".