The determination of a threat is based on perspective. A marine would not likely feel threatened in comparison to Kyle.
Also different circumstances. False stepping isn’t the same as chasing and yelling violent threats.
We’re talking about a marine armed with an AR rifle and an unarmed 5 foot 3 guy?
I was in Army Signal Corp but remember some of my training. I would bet in the back of his mind the Marine was deciding whether to respond with a vertical butt stroke or a horizontal butt stroke if the idiot came after him.
Rifles make pretty good clubs.