Never really understood why Horde players always try to frame this as a 'misunderstanding'. Sylvanas had her troops pull back and let the Alliance tank the brunt of the demon assault to cover their retreat. Whether she did it purely to save the lives of her men or if she was intentionally trying to get the Alliance army wrecked is pretty immaterial and some members of the Alliance being upset is justifiable regardless.
Don't really see the point in trying to twist things around to frame it better for whichever faction you happen to like more.