just like i said in previous post.
you put more weight than what your body could move and do efficiantly, there for you gained muscle to move the amount you pushed on yourself. but you also (from what you wrote) did alot of full body workouts. rows,pullups,presses all use a varitety of dif muscle groups to do. there for everything is getting worked.
im not really trying to debate here, i just dont want this kid to think if he wants big arms hes just gotta do leg excersizes. to be short, he just needs to add weight each time along with keeping good form and size will come. (keeping in mind his diet allows for growth too.)