IMHO, it was a request that was not well considered or thought out in the first place.As I suspected, Vietnam rejects US request to stop their reclamation, though I find it a stretch to say it's merely to prevent erosion of current infrastructure when pics of Sin Cowe Island shows it doubled in size. But the answers about sovereignty is no different than China.
The very idea of making such a request when shear common sense told you that it would not be acceptable is pure folly. It has placed the US in a position of looking foolish...which can only erode position and influence.
Oh well...things are going to play out as they do.
China has done phenomenal work in the SCS. Eclipsing all other comers by literal orders of magnitude. Yes, Vietnam had done some reclamation. Taiwan has done a little. The Philippines too...but all of them combined pale in comparison to the PRC projects.