Well well well, that was a pretty neat chapter.
When Rukia gave him his powers she said "The percentage of success is not high", makes sense that they'd have a safer method, perhaps this guy didn't literally create them but instead created the safe method of obtaining a Zanpakuto.
The Arrancar that had the swords were the ones that Aizen modded right? He was pretty good at SCIENCE!!!! and of course he has the god particle Hōgyoku. It wouldn't surprise me one bit if he just stole the Zanpakuto recipe with his hypnosis whatnot decades ago.