Oh, no-one is doubting that you won in one turn. What is being questioned is your understanding of the game's rules (I.e. if that would have been a win if you played by the official rulings and restrictions). As it is, there is no legally playable six-card combination of cards in that deck that would let you win, unless your opponent does something completely dumb like activating a bunch of self-damaging cards and doing most of your work for you. Care to specify how exactly you won? What cards did you use, in what order, and what did your opponent do? Please tell me you played with 8000 LP like the game is supposed to be done? Something is obviously off there. xP
On a side note Frostweaver; dragon's can OTKO without Future Fusion, though. Just Card Destruction two Rare Metal's (or other big beater types), a Spear Dragon for piercing and a Mirage Dragon for trap negation, then discard a fifth with any given discarding cost (Such as Dark World Lightning or Lightning Vortex, or just plain summon it), then play Dragon's Mirror and Dimension Fusion. It's all doable if you draw the right cards, just highly unlikely. Without Five-Headed there isn't a chance in hell, though.