I too heard that story but on TV. The reason he didn’t shoot was because he just couldn’t shoot him in cold blood.
The reason the American Backwoodsmen gave Major Ferguson an honorable funeral while leaving all the others to rot was that Ferguson was shot 11 times and got his foot caught in the stirrup and was dragged a long way. Even then he tried as he was dying, to get to his pistol to fire one more time.
I guess the Americans appreciated anyone with that much toughness and courage so they gave him his funeral.
Ferguson was one tough dude. I’ll pull out my Leckie book and see if I can find it. I also loved the story about Colonel William Washington crossing swords with Bloody Ben Tarleton at Cowpens. IIRC, there’s a painting of that encounter.