The rarer skulls are elongated and lack the sutures typical of normal human skulls. These are cousins of ours with an unknown father, they have twice the cranial volume of a normal human which is not possible thru head binding. Head bound children were our ancestors attempts at looking like them, emulating them. Powers are possible but the look afaik was cosmetic, trying to copy another being.
'Giants' are real as well, hidden from us just the same. Call em whatever you want, nephilim, aliens, whatever. Doesn't matter to me til all this shakes out and I dont think the distinction even matters. Different terms for the same thing, whichever turns out to be true.