Pierre isn’t a soldier and doesn’t have a natural eye for a battlefield, so when a problem seems obvious to him, he assumes there must be crucial details he’s missing. In this case, he’s right: there’s a reason the Russian soldiers are clustered at the foot of the empty hill, but Bennigsen, assuming his read of the situation is correct, repositions the troops to his liking. It’s an example of miscommunications and assumptions having an impact on battle outcomes, even more than clear orders do.