I would call him heartless for stealing supplies, I wouldn't call him heartless for watching the people die. What was he supposed to do in that situation? He would have either died or expended enough energy that he would have died if he got into another fight.
I think otherwise first come, first serve now that the situation has become utterly chaotic so i can't blame him for hoarding the supplies for himself in any case lives are much more valued more than anything in the current state of their world with that said he doesn't necessarily need to step in and fight the enemy head on to help , there are other ways like say perhaps, cause a distraction leading enemy astray enough that he won't be found out while the others make a run for it something like that.
Man. .this dude is heartless and just watched people die not even bothering to help then again im here for the dog