Jaki, on a whim I looked up your grandfather in Hungarian Wikipedia (https://hu.wikipedia.org/wiki/Erd%C5%91s_Rich%C3%A1rd),
which has a link to (and basically quotes verbatim from) his entry in the Hungarian Jewish Lexicon (http://mek.oszk.hu/04000/04093/html/0245.html):
Erdös Richard, opera singer, born in Budapest 1881, died in the same place June 10, 1912. He grew up in the Jewish orphanage and already sang in the synagogue choir as a child. From there he got into the Opera's choir, and then having finished his studies at the Music Academy and on a state scholarship in Munich, he became a private singer with the Hungarian Royal Opera at the age of 25, as the direct successor of David Ney. However, in 1911 he contracted with the Frankfurt opera. In the spring of 1912 he joined the Bayreuth singers as a guest performer in the People's Opera's Wagner Ring cycle, to great acclaim, but due to severe heart trouble he fell ill during a performance and died a few days later. Chief roles: Sarastro, Brogni, Mephisto, Hunding, Hagen, Daland, Marke, Pogner, and head priest (Aida). At high holidays he sang in the Dohány street synagogue.