Afaik theses are just a lucky occurrence and not bred by parents. Similar to the first albino perals.
But no if you cut off an arm it certainly wouldn't be genetic and magically transpired into offspring.
All I know is that it's special needs and needs special attention. It's a cool fish but something tells me this is not normal and wasn't genetic.
Many crazy breeders overseas cutting up fish and experimenting to make cool newer ones.
If it's genetic someone tell me which gene it is and the genetics behind it. I want to know if it's X linked AR AD and so on. Anticipation if it occurs or not.