You're supposed to see the world through the memories of a 9th century Viking (who also happens to be a great figure of the Nordic mythology), of course the invasion of England will be portrayed in a positive light and Anglo-Saxons would be seen as inferior people. It's a Triple-A game featuring gods, diverse Vikings, and a dude with an axe in his head; if one takes it as a reputable historical source, I say the problem is them, not the game (although IMHO there's many things wrong with the game in general).
Anyway, perhaps it's a fair point to make if your blog is called "A Collection of Unmitigated Pedantry"...