If the hydrogen and oxygen get redistributed in the wrong way, the room will fill with water and you drown.

That's basically what they think, yes. That it interrupts the flow of the air, as if capillary action was needed to pull air into your lungs. I'm not sure how the myth started but at one point they were selling fans with special guards or something to protect against the imaginary risk.

Of course, I might be wrong - I read about this on the internet.