I hold a copy of Maton's excellent reference to foreign awards and realised that GFW was not listed there. The diary writer was a freshman officer in the RAF at the time of making the entry, so I suspect that he makes the CdeG reference in ignorance as to what various middle ribbons indiate - or during one of numerous pub visits WWI war talk got a bit carried away!

PS: Medal cards are better viewed on rather than TNA. The latter copied only one side of the cards whereas the former site shows both. Occasionally the reverse side can throw up additional information.