The author is really trying to shit on the guy for being "shortsighted and hot-headed", but the problem here was that he was lacking in information.
How was he supposed to know that the other knight was hiding "classified information about witches", and was trying to "hint to him" that they should retreat in the face of a Witch? He couldn't. He had no idea wtf was going on, and reacted accordingly. And even if he DID had that information, and DID cooperate with the other knight...What do you think would happen? The dark-elves were clearly already waiting in ready in an ambush. The humans were going to die no matter what.
TLDR: All of the "you're so stupid" lecture is plain bullshit. The only true reason it's there, is because...Well, they're evil. Surely they like to shit on people.