It's not horrifying when dreaming. It's like "yup, 7 fingers, totally normal, let's move on".
In dreams, I've seen people vibrate drastically until they become part of the scenery. Or other insane and horrible to describe things. However, to "myself" in the dream, that was not as surprising as my recollection of it.
A lot of the motional subsystems in your brain are turned off when you dream so you don’t react to things as you normally would. Nightmares, etc happen when those subsystems stay on for some reason (PTSD, for example). See Chap 10 (IIRC) https://amzn.to/3DzSLva
I think you missed that they were pointing out a typo, the original poster said '5 (fingers) per finger' not the intended '5 (fingers) per hand' (and before anyone points out that it should be digits, yes, I know, take that up with the original poster too).
In dreams, I've seen people vibrate drastically until they become part of the scenery. Or other insane and horrible to describe things. However, to "myself" in the dream, that was not as surprising as my recollection of it.