Can someone clarify this statement from the original nanoID site (https://github.com/ai/nanoid) for me? "random % alphabet is a popular mistake to make when coding an ID generator. The distribution will not be even; there will be a lower chance for some symbols to appear compared to others."

If random is picked such that it's in the range of alphabet (i.e. 0 to 25), then the bias should not exist, right? Is that what he's alluding to? Thanks in advance.