I don't think you did.

Some blind people listen to things at superhuman speeds, but not all blind people. Using a normal reading speed is a sensible choice for an ad trying to appeal to blind people since you don't want to intimidate those who don't use superhuman speeds.

Going from that to "heh a sighted person made this because it's normal speed" is simply incorrect.

It was the sort of statement an HNer might make to showcase some trivia they have about some other group, but they oversold it.