The calculation is incorrect I believe, the probability of the profit being worse than it is is around 7% according to my calculations.
Could you please point out where my mistake is, because I looked at it again and I can not spot it. Also I don't see where you are wrong either although the method you are using is unfamiliar to me.
And your method is unfamiliar to me! I have no idea where "Variance of 18 000 bets of 200BTC at 49.5%: 200 * sqrt(0.495*0.515*18000) = 13 500" comes from. My method is to simply apply the central limit theorem.
In any case, the exact number is not too important. The important thing (to me) is that the probability of nakowa winning this much under fair circumstances is not out-of-this-world, yet it's important to keep in mind that nakowa COULD theoretically be cheating (seeing the server seed for example). Personally, I do not believe this is happening.