Let's go over real quickly why. In small data-sets, there is more statistical variance. More opportunity to go against the theoretic odds. In classic blackjack, playing Basic Strategy, the odds are about 99.4%. The more hands you play, the closer you are going to get to 99.4%. This player defies the odds of small sample sizes.
That's not how probabilities work. The chance to win or lose any individual game is the same regardless of sample size.
Casino's sample size is large enough anyways so even accepting your premise they still don't have anything to worry about.