Of course, a murder was and is considered a murder then and now, but we will not understand the people of those times if we anachronistically characterise their deeds with the modern concept of "genocide". Whatever they did, it was no genocide, as the word and idea in its current definition did not yet exist. On the other hand, if the did the same things today, it would be genocide.
That killing innocent civilians was generally regarded immoral doesn't need to be mentioned. Killing civilians for retaliation is a crime since about a hundred years ago (Hague Conventions, I believe), but - as far as I know - wasn't considered one in the Napoleonic times. Killing an enemy who wanted to surrender on the battlefield was no crime, but justified by the very circumstance that the battle was taking place. If we characterise the killing of an armed civilian or an unarmed enemy on the battlefield as murder, we miss the point that these acts were justified (though not necessarily "good") within the context of the moral standards of the period.
Napoleonic Soldiers (and people in general) had their own sets of moral standards, which were different from our modern views at least in parts, and of course not all of them had identical standards. Different doesn't mean better, and doesn't mean it could or should be used as justification for our own deeds today.
Maybe, in 200 years, German and other nations' soldiers who serve nowadays in Afghanistan will be called murderers or killers by a more pacifist world, but does this help to understand why they have become soldiers and why they act as they do ?