Basic Normal Distribution Question

[Munga30]

In a small stakes thread, a poster asks whether his breakeven first 10K hands at 2/4 is just a downswing. Several posts shouting "meaningless" and "sample size" ensue. Gaming Mouse says it's not meaningless, just inconclusive. He says a player with a true win rate of 1.5 BB/100 has a X% probability of breaking even (or worse) after 10K hands and a 2 BB/100 player has a Y% probability of the same. (FWIW, I think X was about 16 and Y was about 9).

How were these probabilities calculated? I *think* if I choose a confidence interval where the lower limit is zero, the answer is just 1 minus that CI. Terminology may be a bit off, but is that about it? Please instruct. Thanks.