In truth, it's a pretty pervasive myth. We've had discussions on here over incidents where even relatively highly qualified referees seem to subscribe to this belief - possibly this one, although I think it's more of a misinterpretation of DOGSO than anything else.
The weirdest example of it that I've come across was in a youth tournament in Denmark one time, where it was actually written into the rules of competition that any handling offence by a goalkeeper outside their penalty area was a mandatory red card. I was coaching, not refereeing in the tournament and I remember it distinctly as our U-14 goalkeeper was sent off for it in our first match (clear non-DOGSO, there wasn't an opponent even in the same post-code). Our head coach insisted on going and querying it with the tournament judges. I expected it was going to be explained as a non-reversible referee judgement call but instead they pointed to the tournament rule-book and said, "Look, here, it's part of the rules."