I was hoping that he purposely pretended to be out of stamina for 2 merc guys before the last one, but alas, the MC's not THAT clever. Worked out nicely against the last one though, who didn't want to get caught in the same trap but should have bum rushed.
I actually think that leaving the soldiers alive was a good strategy. Putting aside the Japanese no-killing trope, wounding enemy soldiers and stealing their supplies is a great way to slow down an army unit, as not only do they have to resupply like was said, but having to care for their wounded means they either slow down or split up. In addition, if there are people left alive, they can tell cautionary stories that will also help prevent rapid advancement into unknown territory.
This wouldn't have worked with the mercs though, because no merc is gonna risk his neck to go find out who wiped out an entire company without some serious pay or insurance, and that group was probably the entire group. Better off killing them all.