Validity of the sample size is not determined by its fraction of the whole population. I don't know the formulas and I'm not a statistician. Maybe someone can drop some citations.
I generally agree with this just from a perspective of personal sentiment, it does feel wrong.
But statistically speaking, at a 95% confidence level you'd be within a +/- 3.5% margin of error given the 791 sample size, irrespective of whether the population is 30k or 30M.
You should read more about statistical significance. Under some reasonable assumptions, you can confidently certain deduce things with small sample sizes.
From another perspective: we've deduced a lot of things about how atoms work without any given experiment inspecting more than an insignificant fraction of all atoms.
TL;DR: The population size (25e6 total devs, 1e80 atoms in observable universe) is almost entirely irrelevant to hypothesis testing.