I suppose it does get into terminology questions of “advisory group” versus “think tank” versus “environmental organization”. But I think at the end of the day, the reality is that the kind of work the round table did was often to speak to various participants in the system, to do analytic and economic research, to do comparative international research—just some examples—and on the basis of that, to make recommendations to the government.
While you're right that certainly they differ from other kinds of organizations—in that they were established by an act of Parliament and reported to Parliament through the Minister of Environment—the types of work, the types of analysis they did, and the idea of trying to base recommendations on that analysis bears many similarities to the kind of work done by environmental groups, think tanks, academia, etc.