It sounds like WoW got the real-world instructions correct. Playing dead can be a way to survive an animal attack, and is consistent with some of the recommended extreme situation survival skill techniques. It sounds like the moose might have been scared, or defending territory and when the kid played dead, the threat to the moose disappeared, so the moose stopped its attack. I suspect that it also helped that humans are not a potential prey animal for moose. With another animal such as a pack of wolves or grizzly / polar bears, this might not have turned out so well.
I am sure that some of you will not like what I have to say next, however, I'll caution that what the boy did is consistent with real-world nature survival skills. Think "Survivor Man" or "Man vs Wild", or techniques you learn in "serious" survival courses.
If, however, you find yourself in that kind of situation and you employ techniques from gaming, prey that the gaming techniques are consistent with real-world techniques.
If you know you could be in a situation like this before you actually find yourself in such a situation, the best thing to do is to prepare by studying the appropriate survival skills.