They Didn't Give PPM Levels
What I do know from the documentary is that both the Methane and CO2 levels were estimated rather than measured. The methane level was based on assuming the C12 spike was caused by methane and the CO2 was estimated based on lava generated in the Siberian Traps. It wasn't clear to me whether the amount of lava was known or also estimated. The impact of the CO2 and Methane were then estimated using climate models. It's not a slam dunk conclusion just the best explanation given the data available.
Regards,
Mark