I ensure you I have never thought so.
Don't worry, I know you didn't ;)
Speaking that I don't consider someone who thinks that there was a cultural isolation as being mean or anti Polish or whatever. Just uniformed that's all.
That's about it - uninformed, and indifferent.
I've always considered it interesting how people from the capitalistic countries of that time imagined living under communism. Certainly many have some views influenced for instance by the media informations they were given in those times, right?
It was a long time ago, and I can't remember that much about the media reports, but I don't think that "culture" was really mentioned that much. But I don't think that this would make UK people think that Poland had no culture. I think most people weren't interested, that's all.
It affected families like ours, of course, because we had relatives over there, so we kept ourselves informed about life in Poland.
I think that most people would have thought of Poles as poor and oppressed, but not necessarily uncultured.