I doubt if they'd use it that way, because it's clearly enough not intended as a scientific survey, how could it be?

I just did it again, trying to answer how I imagine a fairly toiugh minded, but not excessively so, conservative might answer - and I came out Economic Left/Right: 5.38
Authoritarian/Libertarian: 1.90

Which was more or less spot on Michael Portillo on the chart. So perhaps it's not so far out.

But I still can't see how a question about whether abstract art is rubbish or not ties in with either left/ right or authoritarian/libertarian. There's no reason why someone at the opposite ends of both these ranges should't give exactly the same answer to a question like that, and it might be either answer.