Notice how this doesn't bar it from approximating human discourse. In fact, it's a staple of how we communicate and would have to be one of the essential tools in an impersonator's toolbox.
"The above quote couldn’t be more incorrect despite sounding intelligent" could be leveled at comments on any HN submission.
Though it can't confirm that the speaker is incapable of reason, else us humans would be in big trouble. The reason that we know that GPT-3 isn't capable of reason is because we know how it was made.
If we ever achieve general AI, I think it will emerge from as black a box as human consciousness, and we will be back to bedrock on philosophical questions like "are we actually conscious?" and "when does something become conscious?" except now we won't have to ponder those questions alone.