It could be that my memory of hypothesis testing is outdated, but being 1 standard deviation away from the mean isn't evidence of a significant difference in skills.
(If it was hypothesis testing, 1 sigma could be statistically significant depending on sample size. You might be confusing the population variance with the sample mean variance.)
That's exactly what I'm doing - thanks for pointing that out.
1 standard deviation in mean is substantial. That means approximately that 80% of one group exceeds performance of the median of the other group.