Forum:Light and darkness dragon wtf???

Ok so at locals i was playing against a quickdraw deck and he pulls out light and darkness dragon. I activate spells until his attack is 1300 then i hit him with a 1700 attack monster. but instead of him dying he uses book of moon on him and says he chained it to him being destroyed??? i was just like WTF!! and i dueled on and lost. :(   Was that a legal move and why?