It sounds like he is just looking at things on the surface.
If he is referring to the event at the Solitude gate that happens when you first get there. Yes that was an awful thing to see, but maybe he should put a little more thought into it then 'oh no, that guard was right...the other people are wrong'. The outcome of the Ulfric fight was in dispute from the sounds of it, but who is this guard to say that the people disputing it are wrong? Of course Ulfric probably wouldnt have gotten just treatment himself if that guard didnt do what he did, but guess we'll never know now will we?
Also i still stand by what i said about the imperials and stormcloaks. I havent done the CW story yet, but i dont need to do it to know that there are no 'good and evil' sides in a war. As a whole the Stormcloaks might be the good guys fighting for Nord independence, but are you gonna tell me that in all of the Stormcloak rebellion every soldier is a saint? that there are no bad apples?
EDIT: @ OP, best thing to do is talk to NPCs for both sides and see if their dialogue will sway you one way or another.