Extremely odd question! I wonder what provoked it.
Oxford is one of the top universities in the UK. An education in Classics is taken to show understanding of language, history and politics. Many classics scholars will apply for civil service jobs, including in the foreign office. A common first posting for might be as a third secretary. It gives the person the chance to improve their language skills (Arabic in this case) and gives them a chance to prove themselves. If successful they can reach high rank. I might notice that the current foreign secretary holds a classics degree from Oxford.
Cowper-Coles is exactly the sort of person who one would expect to find as Third Secretary in the Diplomatic mission to Egypt., either in the '80s or now. I notice that Third Secretary was his first assignment, and he went on to much more high profile jobs later. As richardb says in a comment "He went straight from private school [and] Oxford to being a junior civil servant. It's almost embarrassingly stereotypical"