It would make sense because reg looks very human and has faetures that aren't practically useful like a belly button or a penis, reg also is completey immune to the curse, if hes like the ancient people of the abyss than that would explain how some of the ruins in the show are able to exist, as some of the structures would cleary require immunity to the abyss's effects. Like the skymill and elavator on the fifth layer, there are also towers and strange column like structures in the 6th layer that would be near impossible without such immunities, it would also explain why no one has ever seen beings like Reg before Other than a select few ofc Anyways reg also seems be made up of both organic and mechanical features indiccating he was possibly human once or atleast similar Reg can also eat normal food and be charged with electricity which would make sense for a civilization that exists in such a hostile environment Anyways thats my theory, feel free to debunk it thouroghly