[kazinator]

The stereotype is statistically true in the sense that many (probably most) programmers have a mother who isn't a programmer. Secondly, most programmers' mothers are 20-35 years older than they are. So even if they are also programmers themselves, they are senior, which means many of them are probably not coding any more (or are possibly retired,even). They wouldn't be able to build a web site without ramping up on how it's done. Nobody is saying that anyone's mother is an idiot.

What is troublesome, though, is that the example person is invariably a female ancestor or relative: it is always "mother", "grandmother" or "kid sister" ("encryption scheme that will keep out your kid sister but not the NSA").

Many programmers have a father or grandfather who are not programmers, or technologically savvy. Many have a prying kid brother rather than kid sister.