Hmmm. Sherries have sugar; some of them have quite a bit. Although, in a way, maybe it is the right answer because sherries aren't fortified until the yeast has converted nearly all of the available sugars. It's not up to me, but you probably gave the answer Chef Petals wanted.
As to your question, you're probably referring to spatchcocking, which, by the way, the OED reports the word as of fairly modern (1785) Irish origin, rather than English and certainly not Old English which is something else entirely.
As a method of cooking, it's undoubtedly significantly older than the first published reference and undoubtedly trans and multi-national. There's no reason to suppose that butterflying poultry originated in the British Isles or any other place for that matter.