I don't know where you get your quote from wiki, but this is the quote from: Battle of the Paracel Islands
http://en.wikipedia.org/wiki/Battle_of_the_Paracel_Islands
Prelude
On January 16, 1974, Frigate Lý Thường Kiệt (HQ-16) witnessed a small band of
Chinese militia on one of the islands called Robert Island. The militia set up a flag and stelae representing the Chinese sovereignty over the Paracels; they were supported by Chinese warships (#389, #396) and minesweepers (#402, #407). HQ-16 signaled the Chinese squadron to withdraw, but received the same orders in return. Overnight the two forces remained shadowing each other but did not engage.[citation needed]
On January 17, some 30 Vietnamese commandos waded ashore to Robert Island and removed the Chinese flag unopposed. Later on reinforcements from both sides arrived: the frigate Trần Khánh Dư (HQ-4) joined the HQ-16; while two PLAN corvettes (#274 and #271) joined the Chinese.[citation needed]
On January 18, frigate Trần Bình Trọng (HQ-5) arrived at the scene carrying the commander of the South Vietnamese fleet, Colonel Hà Văn Ngạc. The corvette Nhật Tảo (HQ-10) also took its place, moving in cautiously because she had only one functioning engine at the time.[citation needed]
Military engagement
In the early morning of January 19, 1974, Vietnamese troops from the HQ-5 landed on Duncan Island and came under fire from Chinese troops
after opening fire first on the Chinese while advancing toward the shores.
Yeah, a clear matter of Chinese invading Vietnam territory.....