It seems your are right about going back to Germany
DESCRIPTION HGF SCHILLER. REPATRIATED 16/5/1919.
That record description is from NAAIRS Repatriation could be voluntary. Depends on why he was in South Africa. You will have to get a copy from the archive.
Find the address here
Hamburg, Germany, Deaths, 1874-1950 are available on-line records for Hamburg.