Gen Z is turned off by onscreen sex, a new study finds. Those born between 1997 and 2012 apparently prefer to see platonic relationships in film and TV.
The person you responded to doesn't understand statistics. As long as your sample is random and unbiased, you don't need to sample the whole population.
Think of someone cooking. They just taste a little bit of the food to adjust the spices. If they mixed it up evenly, they don't need to eat the whole thing to get an idea of how it tastes. That is the basis of random sampling.
There's a weird online phenomena of people with no knowledge of statistics criticizing the sample size of studies they disagree with. Of course that criticism never comes up when it backs up their world view.