It's looting if your enemy does it. And yes, passants, and generally civilians, are always in for bad times during war.

An army that wants the peasants alive (which is by no means all) can only take so much of the food the area produces in a year, if a previous army had already been through that was probably zero.

Of course for Peasants you need to come up with a way to hide most of your food, while having what looks like all your food in what looks like a poorly hidden place where the army can force you to give it up. (good luck)

The army that is passing through does not have reason to care about keeping peasants alive. Moreover, soldiers were brutalized enough not to care.

That demands on the amry's goals. If they want land to settle down and farm then death to the locals. However if they want tribute dead peasants pay no taxes.

Also: "Sorry, we've already been pillaged!" (It might work.)