Plum in Latin is prunum, plum tree is 'prunus' and down the ages to this day dried plums are 'prunes'. Claudio is from the Patrician family name Claudius, derived from the word claudeo meaning 'to limp' or in a figurtive sense 'to be defective'. Being a family name, only the original Claudius was limp, just as only the original Smith in a line was a smithy and subsequent generations of Kennedy's may or may not have been afflicted with the big ugly head that created their surname. It's not a PC feel-good meaning but it is what it is, Claud- means 'lame' or 'defective', Calvin means bald, Caden means barrel-shaped - such is the lot of names that began life as nicknames.
Robert Graves wrote a novel, otherwise known as a work of *fiction*, and he can say anything he likes in his novel because it doesn't have to be correct, only readable and hopefully interesting. When researching, it's best to stick to the non-fiction section ;o)