yea the optomistic nature seems to be contradictory to everything else we know about andalites, i guess because of the trouble it got them into maybe they feel ashamed about it or something, so the warriors compensate by being arrogant
maybe its that civilian andalites dont really have interaction with other species, i assume, seeing as how its so difficult for the yeerks to infiltrate the homeland i always assumed things were locked up pretty tight, and i cant really see them trading with another species and admitting that they can do something better than them haha