That zombie was grinding XP the whole time after he got out of the mud.
He probably bought the 'Use Gun' ability with his Souls and was packing that heat Carl dropped earlier, but when he saw the area boss was just a random old man, he decide to save the ammo and just attack without anything equipped.
He posted the vid on Youtube to prove his mad skillz.
Another episode with some really bad writing.
Dale has to die in this episode, so let's just have him wandering around in the dark by himself while everyone else is executing a prisoner. Because, you know, that makes perfect sense.
One of the strengths of the original story is that, more often than not, Kirkman managed to avoid the standard horror trope pllot conveniences. The comic (which, remember, I still don't know even exists) wasn't flawless in avoiding them, but more often than not it did a pretty good job of coming up with reasonable scenarios for character death.
In this season, we've already seen way too many instances of characters acting stupid for no reason other than to initiate a plot necessitated zombie attack.
This production is troubled. It feels like too many different people, with their own interests in the show's direction, are involved in the creative process. It has all the telltale signs, which start with certain parts being very smartly written and well acted juxtaposed with certain parts being worse than fanfic contrivances.