I would assume they're referring to spyware that's sophisticated enough that it was likely state-sponsored, a la stuxnet, as states usually are the only entities with the resources to develop spyware of that level.
I don't buy that for a minute. There are so many amazing developers out there who could absolutely do this independently.
Capable of writing the code, yes I agree there are others out there more than capable. But part of what makes stuxnet and others of its kind limited to Govt. sponsored is the amount of funding required to do the research to write the code. Very few malware developers are going to go purchase a Siemens nuclear refining centrifuge (plus controlling equipment) so they may reverse engineer it and figure out how to break it. Someone had to buy one, then realize if you stop it suddenly enough times it will break.
What kind of features are included in government sponsored spyware vs the regular kind?
One or more Zero-Day exploits
Pretty sure the author means that NSO Group's primary customers are government agencies.
That said it's still more of a buzzword than a qualification.