Kinmen is about 3km from the nearest populated, road-connected part of China (小嶝岛). The article claims that fishermen were caught within "1 nautical mile," equivalent to 1.852km. You're free to do the math.

Kinmen is notorious for being a KMT stronghold, which might explain why during the last election the government prevented some Kinmen residents from returning to the island to vote. There's been a distinct policy of disenfranchisement from Kinmen by the DPP.