the concept of the modern surname developed post Norman conquest of England and became fixed orthography with the advent of 19th universal literacy- patronymics were the basis of names prior to this development (seen for example in the old Manx nick names - tom son of tom etc) - Welsh 'surnames' still changed from generation to generation to the 19th C.
The origin of the name Kieg can be seen in one of the earliest written documents in Manx records - remember however that these were written by English scribes and reflect the conventions of his background - see www.manxnotebook.com/manxnb/v05p020.htm for Moore's derivation of name.