To differentiate between soldiers and peasants, Aatrox refined control over the intention to kill. In the beginning, he only knew how to feel the intention to kill, after this battle he learned to feel who was exhaling this intention. Thus, those who intended to kill high were considered soldiers, and those who did not were considered peasants.
Some peasants with a lot of intent to kill died, just as some guards survived, but Aatrox didn't care. These people became grateful to him and gave him the nickname Lord of War after seeing how he alone waged a war against an entire kingdom and won.
...
Now, when Aatrox saw the number of guards that the Price family had placed on patrol, he instinctively tried to feel the intention to kill them. And as he expected, most of those people weren't really guards.