It’s a little odd how everyone is misreading this comment.
They are not saying that introverted and extroverted characteristics did not exist in people, they are saying that people did not run around proclaiming their introverted or extroverted status in the same way they do today and they didn’t use it to rationalize behaviour to the same extent.
They are not saying that introverted and extroverted characteristics did not exist in people, they are saying that people did not run around proclaiming their introverted or extroverted status in the same way they do today and they didn’t use it to rationalize behaviour to the same extent.