He named first Kant and later Wilfred Sellars as examples of the sort of epistemologist he has in mind. Let us use the broad term "constructivism" for the broad PoV that Kant and Sellars share, and that bemuses our Stoic.
Ciceronianus, if I understand him, then proceeds to the assertion that such constructivism is either pointlessly obvious or wildly wrong. The obvious and uninteresting point is that "we are human beings, and as such interact with the world as human beings do." Yet those who are most serious about urging that "they shape the world" seem to want to go much further than this, and that furtherness is what bothers Ciceronianus.
I contributed a thought of my own to his comment section.