If you are introduced to 5 blue-haired Xians but no black-haired Xians, you might infer that all or most Xians have blue hair. That is a pretty obvious case of sampling bias.
If a-priori you had no reason to expect that the population was dominantly blue-haired then you should begin to suspect some alternative hypothesis, like your sampling is biased for some reason, rather than believe everyone is blue haired.
If a-priori you had no reason to expect that the population was dominantly blue-haired then you should begin to suspect some alternative hypothesis, like your sampling is biased for some reason, rather than believe everyone is blue haired.