https://www.wondrium.com/king-arthur-history-and-legend?tn=632_tray_Course_1_0_2444&lec=3

Historia Brittorum, chapter 65, states that Medcaut is the name of the island on which St Cuthbert died. This was not Lindisfarne, but the nearby, smaller, island of Inner Farne. I believe this works better with the proposed etymology - Inner Farne would make a suitable location for growing medicinal plants which could be dangerous to livestock (or careless monks). It would also be a suitable location for isolation for fear of communicable sicknesses. Cuthbert himself, of course, endured severe symptoms while there (notwithstanding his primary reason for contemplative isolation - indeed his desire for solitude could well be linked to his illness).