I think what the article meant to say was that, for the same number of samples, the p-value when you have delta=50 (the difference between groups), stdev=10 is the same as the p-value of delta=0.5, stdev=0.1.

Depending on the study, finding a delta whose p-value is significant does not necessarily mean that the size of the effect (i.e., delta) might be significant enough to be useful.