So who do you blame? There is no one else to blame - the good news is he seems to now realize how dangerous what he did was. Hopefully, his sharing and the subsequent discussion here will prevent others from making the same mistakes!
The extremely poor training he received. If I get someone who resembles a younger version of myself, I'm going to describe in the best detail I can the consequences of not abiding by the fundamental principles of safe diving. While being young gives somewhat of a buffer against DCS, it does not making the walls of your lungs stronger, nor reduce RMV, etc..
I have a really low opinion of the average OW course today.
@Matt Spear. No touching of coral. Not for hunting. Okay?