Re: Hang on.. 6 limbs?
No, four limbs. Two large legs at the back, and two rather puny forelimbs. The wings are part of the forelimbs (or vice versa). It's clearer on the picture of the fossil.
This does raise the question of what use are wings that don't enable you to fly, I've tended to assume that modern flightless birds have wings because they've inherited them. This creature and its kin seem to have developed wings as a sort of decorative feature on the forelimbs. The implication is that wings (and feathers, too) evolved in response to some non-flight-related selection pressure and then turned out to be useful for flying.