Both were owned by Meccano, and the French factory predates Dinky Toys - it was opened in 1921 to produce French Hornby and Meccano. I have read that part of Hornby's initial success was due to anti-German sentiment after WW1 as before the War most toy trains sold in the UK were German. Perhaps the French factory would have been able to capitalise on the same feelings, or maybe some way of avoiding duties?
Although both factories were pretty much separate entities under common ownership with the Dinkies at least having pretty different product lines I think there has been evidence of joint working, with drawings for some French Dinkies done in Liverpool etc. Some French models were made from UK dies - the Blaw-Knox is one example I can think of.
I'm sure Chris can elaborate further
