The Army Medical Department in M.&S. is a complete nonsense. The authors had not received full details of services before it went to press.
Even then an erratum slip was issued as on page 370 a number of names that should have followed the entry for the A.M.D. appear followed the listing for Army Hospital Corps. Included in the number is Surgeon-Major J. H. Reynolds, M.B., V.C., which is where I think the film got the information from.
That said Dr. George Henry Kenneth O’Callaghan, then a Civil Surgeon served with the 2nd Division, and no he does not appear in M.&S. Joined the A.M.D. In March 1880.