You are right, this article is more sloppy science that the global warmers can use to claim the science high ground. Another example besides yours, sure methane and CO2 are "mostly" natural origin in that their cycles have large natural inputs and outputs from the atmosphere compared to our inputs. However, the main reason both are rising is manmade inputs. How much of the increase is manmade versus natural needs to be resolved but it is not negligible.
Sloppy article, I think. BTW, wouldn't N2O be dinitrogen oxide?