I don't get it

Devon and Cornwall are known for having silly disputes with each other. The Scone Debate (see pic) was one such example; another one is accusations of Cornwall that Devon keeps aping their heritage, e.g. the flag of Devon (St. Petroc's Cross) is a 21st century invention but it quite directly copies that of Cornwall (St. Piran's Cross) which has been consistently used since the 19th century and is itself based on some records of regional banners from medieval period