Does one move make a game?

I was watching the following game during the last round of the 2014 Sydney International Open. Of course this was because one of the players was my son, but also because of the choice of opening (the Frankenstein-Dracula variation). Having played the black side of of it on occasion I was interested to see how it would turn out. Once White played 7.h4 I figured it would be a routine hack down the h file with an eventual mate on h7 or h8.
By the time I returned to the game the players reached move 20, and to my surprise Black had weathered the attack and looked to be a solid pawn up. It was then that White uncorked 21.Rxd5 which on the surface looks like a brilliant move. Certainly it posed enough problems for Black that White looked liked he'd reached a winning ending after lots of material was exchanged, and when I saw the players shaking hands I'd assumed Black had resigned. In fact White had offered a draw on move 30 and Black had wisely accepted.
Analysing the game later (with the help of an engine) it turned out that both sides had better moves, but if they had played them, it would have been a completely different (and less interesting) game. And most likely, White would not have had the opportunity to play Rxd5!!.

Puccini,Jack - Press,Harry [C27]
SIO Sydney, 27.04.2014

1. e4 e5 2. Nc3 Nf6 3. Bc4 Nxe4 4. Qh5 Nd6 5. Bb3 Be7 6. Nf3 O-O 7. h4 g6 8. Qg4 Ne8 9. h5 d5 10. Qg3 c6 11. d3 Nf6 12. Bg5 Nbd7 13. hxg6 fxg6 14. Qh4 Rf7 15. Ne4 Nxe4 16. dxe4 Nc5 17. O-O-O Nxe4 18. Qxe4 Bxg5+ 19. Kb1 Bf5 20. Qxe5 Qf6 21. Rxd5 cxd5 22. Qxd5 Raf8 23. Ne5 Kg7 24. Nxf7 Rxf7 25. Qxf7+ Qxf7 26. Bxf7 Kxf7 27. Rxh7+ Ke6 28. Rxb7 Be4 29. Rxa7 Bxg2 30. a4 1/2-1/2