Their conclusion is that the speed limit should be increased; there are other reasonable conclusions one might draw, but I would argue against the one that follows from your comment: that nearly every driver on the road deserves punishment.
I would be very interested in if people would then go the reasonable new speed limit or if they would continue in their speeding flocks and only travel even faster. To me it seems like their speed is mostly something they evaluate relative to the rest of the drivers and not to absolute speeds so it'd take quite a change in behavior.
As for [0], the traffic back-up proves only that the vast majority of people on that road are speeding.
My take on it is that when the speed limit doesn't match the 85th percentile speed of actual drivers, something should be changed. Sometimes, (often, in my view) it's the speed limit. Sometimes, it's the design of the road, especially in cases of neighborhood streets that are shaped like highways. Sometimes the answer may be highly-visible traffic cameras, as the advance warning and certainty of punishment will slow down almost every driver.