It's confusing wording but I think the person he was responding to was saying that he had a harder time comprehending while sober, whereas he has a harder time comprehending while high.
As I understand it, the first person had a harder time comprehending while sober, because of his regular pot consumption. Compared to how well he comprehended sober when he didn't regularly smoke. So both think pot affected their comprehension, although one feels more affected when high and the other one when sober.