The key finding was proof the ice age started 10 million years before the first evidence of high CO2 levels:

"Saltzman and doctoral student Seth Young found that large deposits of quartz sand in Nevada and two sites in Europe -- Norway and Estonia -- formed around the same time, 440 million years ago. The scientists suspect that the sand formed when water levels fell low enough to expose quartz rock, so that wind and rain could weather the rock into sand.

The fact that the deposits were found in three different sites suggests that sea levels may have been low all over the world at that time, likely because much of the planet’s water was bound in ice at the poles, Saltzman said."

---
Even if your opinion differs from the scientists on whether the buried organic carbon shows lower CO2 levels, then we still have a situation where the ice age started in an era where the CO2 levels are unknown. They are resolving this issue:

"Though scientists know with a great degree of certainty that atmospheric CO2 levels drive climate change, there are certain mismatches in the geologic record, such as the Ordovician ice age -- originally thought to have begun 443 million years ago -- that seem to counter that view."

Not many climate doubters would dispute this statement, instead they dispute (lamely) whether the current level of forcing is sufficient to cause change.

The status of the evidence is that much supports the idea that we are having dangerous effects on climate, with little evidence to the contrary. This study removes yet another piece from that "little evidence" pile. If this study is wrong, the predominance of evidence continues to be that we are taking enormous risks.