It was you to actually started a hostile language; the very thread title you put there, which is not the original title, tells everything (although the article mentions THAAD, I agree).
You can simply see it as an investment due to Vietnam's low cost labor for assembly work instead of a zero-sum game against China.
As for rigs, I would not be surprised your "only" rig would be swept away by the first typhoon in the area. Besides, where will you station your rig, in Japan's territorial waters (200NM around a piece of rock called Okonotoroshima)?
Because China's Coast Guard vessels will gently push it away from China's waters; and you know China CG vessels tend to be heavier than your naval vessels.
Thus, you can be ugly, but you cannot be effective.
As if China is not your biggest trade partner and as if VCP does not pay regular visits.