since there were other survivors who wanted his water, maybe the enemy in the game is other survivors. Trying to survive or die. kill others who will take your supplies. and since you have a bag,(it was in the video) you will be able to hold some equipments. Like
Map
Knife
water
gun??
food
flash light
cell phone
and etc
also his shirts and pants are ripped off so he probably got into a combat or used in some place. because your clothes does not rip that easily.

Plz no gun!
Or, if there has to be one 100%, then give, like, 6 bullets through the whole game.
I don't like the idea of this potential hit turning into a shooter!

And I bet there will be combat in some kind of way. Passive? (QTE) or Active? (Button mash )
It's up to devs.
And clothes could've ripped while climbing rocks or something.
Also, he had light summer clothes, and yes - THESE kind of clothes aren't really the best thing to climb the destroyed city in