Yeah, heard about that. Apparently it was a mistake. Supposedly they sent those out as a contiguency, one store in London had it up for half an hour, then took it down.
Nothing changes until 2021 really, and they agreed a trade deal, so nothing much is really going to change as far as food coming into the country goes, other than the fact that it might get a tiny bit more expensive. Cause problems elsewhere, but food should still come in fine. Won't become Venezuela or anything.