That ferocious looking trophy sized beast would at least need a 30-06 to put it down when charging. Messor would not have a 30-06 with him. Maybe a .308 would have been possible in his hands. And that is why his fight or flight instincts had him to flee instead of taking it on. He simply did not have enough gun with him.

Just glad you did not move around in the dark whilst the snake was still on its way to his snug little space. But luckily puffadder normally hiss and put up a show instead of just striking.

(I am in no way condoning the killing of snakes especially in the wild.)