Unintelligent and/or ignorant people tend to confuse their assumptions for truth.
The fans having tantrums now assumed that Jonathan Williams was the first backup running back on the roster when preseason ended. When that was proven to not be the case, instead of adjusting their perceptions ("wow, it turns out Banyard and Tolbert were ahead of Williams - that's unexpected"), they lash out and cast blame ("Beane and the front office don't know what they're doing!").