For those that don't know, French Guiana being an overseas department of France makes it analogous to Alaska or Hawaii, rather than a mere territory. It's considered a fully-fledged part of France, at the same level as all the departments of metropolitan France.
On your link you can read it's an Overseas Collectivity, unlike French Guyana, which is an Overseas Department. Collectivities have some more autonomy, they can have different laws.
Of course we did, nothing like a good pointless naval dispute. Next thing we know our military will be dropping flags and bottles of booze on their beaches.