the nearest name in 1881 census is
Malew I-"The Military Barracks" HENSBRIDGE William Drummer U M 27 Drummer 103rd Regt born Poplar Middlesex
which (a) would fit with Malew as church (b) explain movement back off island and (c) why the name appears nowhere else on Island in my records at least
A brief description of Castletwon barracks was given on rootsweb B/B but it was the converted George Hotel - the barracks ceased in 1890's - troops were stationed from the regiment currently at I think Carlisle.