Why does Zaroff think that Rainsford "hasn't played the game"?

Zaroff believes that Rainsford has "quit" the game rather than play it out to the death. Rainsford is on the run and finds that his only escape- rather than death- is to jump into the sea. Zaroff sees this action and believes that his one worthy adversary has quit the game and chosen death by the sea rather than playing the game. Little does Zaroff know that Rainsford has not quit the game he has tried a strategy that ensures his eventual victory.