There were no superpowers...Andrew made it up
Think about it. Andrew creates his own surreal world in which he has superpowers, because his mother is dying, he is bullied in school and his father is beating him. And who doesn't want to have superpowers when you're in such a situation like that? In the end, he commits suicide by jumping off the hospital. Let me explain.
He films ALL of it, all of the crazy stuff he does, yet when his father sees it, the only things he says is something like 'they are not your friends'. What the hell? You've supposedly seen your son flying in the sky, and that's all you say? The only reason: he doesn't fly, he doesn't have superpowers. He lives in his own world, filming cheerleaders, but dreaming about superpowers.
The whole film is his big dream. A dream from a lonely, angry and disturbed kid, who eventually wants everybody to die or leave him alone. Why doesn't anyone notice anything if a car magically moves? Because it doesn't, it's just Andrew's imagination. The car crash? The death of Steve? Just Andrew's megalomaniac mind thinking HE did it, that's how disturbed this kid is. The talent show? His ultimate dream to become popular, but in reality, he is propably the one who is filming the stage.
At the end of the movie, he sees his mother die. He goes insane, gets beaten up by the kids in his street and then desperately tries to rob a gas station but gets shot instead. In the hospital, when his father blames him for his mother's death, he just snaps. In his own world, he is the almighty superhero, better than anyone, finally beating his father up. However, in reality, he flees up the building, standing at the edge of the building, waiting to jump.
Matt tries to talk Andrew out of it. In the movie, you see this when they're floating in the air in front of the Space Needle. In reality, they're on the roof, where Matt tries to save Andrew from commiting suicide. Did you notice, when he talks to Andrew in that part of the, he says the exact thing you would say to somebody who's standing on the edge of a building? When Andrew says something like: 'why did you catch him' or 'I am stronger than this', Matt replies with 'Listen, focus!' and even 'this is not a game'. He's trying to get Andrew out of his own world, trying to get his attention, trying to get him focussed. Finally Matt says: 'we can fly away, be famliy, and, more importantly, 'this isn't who you are'. Which is right, since Matt hasn't got any superpowers.
He then jumps with the words 'I'm an apex predator'. The top of the foodchain has no predators of it own, except theirselves. And even in his flight, he images himself destroying the city and its people. He last words are 'leave me alone', and finally, in death, he is.
The actual end of the movie even makes sense now: Matt is going to be a better person, the person he never was for Andrew. He's apologising for letting Andrew go, but it was for the better. The reference to 'what happened down there'?. Maybe the world Matt lived in, or something that happened in their childhood that made Andrew such a disturbed person.
The superpowers were Andrew's Tyler Durden, but the shot really killed Andrew and not the superpowers. Makes all sense now.