Good question Seabear.
Because there is a very strong connection between the British and Dinard, where around the turn of the last century, wealthy British people used to come to the town to bathe. Several roads are named after people like Churchill, and there is a British church, the only one in Brittany I believe. The film festival is in its 36th year. The red carpet comes out and all the usual paraphernalia. Some great films have been premiered there, if I remember correctly Billy Elliot.
Just to say, it's NOT a fish and chip type resort. It's very classy.