It has nothing to do with the city of 广州, some 400 km to the north-east: 广州湾 was originally a local place name on the bay, and France applied it to the whole territory.
history
France occupied the area in 1898 and leased it for 99 years under an 1899 treaty. Japan held it from 1943, and it came back to China in 1945. French buildings still stand in 赤坎.