It's just another way of grouping, as Grin puts it, the "mildly PG" and the "wildly PG."
To me it just seems sort of like nonsense on the level of a quiz in Glamor Magazine quiz or something. I don't understand why anyone puts stock in these levels because the sample size was minute and the questions clearly indicate a particular cultural bias. It concerns me when they are at times elevated to a position of meaning beyond more validated measures like IQ scores or achievement. It doesn't seem to me that at all even consider where 2e children (and that's a pretty sizable part of the PG population) might fit.
Our child is on I guess what you'd call "wildly" PG in terms of scores on IQ and acheivement, SAT scores while young. He's been highly achieving including young entrance into college. As I recall he would get maybe a three on the Ruf scale. So, say I'd gone to these scales when he was a preschooler before he'd been tested. What would my take away message have been? Don't bother?