Any way, it is described in Gishiwajinden (literally, an 'Account of the Wa' in "The History of the Wei Dynasty") that Wajin (Japanese people) enjoy drinking and Doburoku has a long history.
どちらにせよ、3世紀後半の魏志倭人伝には倭人は酒を嗜むといった記述があり、どぶろくの歴史は長い。