It may not have been unusual to be self-taught in medicine, but I think the reader deserves an explanation of how one "becomes a doctor" without going through any process of certification. If this was common practice in those days as well to set up practice as a physician without any formal credentials, the article needs to say so, since a "doctorate" is an academic degree bestowed by an institution of higher learning. If as you say the source uses exactly this wording, then it would be best enclosed in quotation marks, to show the wording is not a careless interpretation by a Wikipedia editor.—