Yes, the fact that a new rocket moved into the South China Sea could incite tensions between China and Vietnam. There is a great deal of tension right now over the South China Sea. The fact that a rocket moved into the area may cause China to take this as a sign that Vietnam does not respect its authority in the area.
Vietnam is "quietly fortifying" some of disputed territory in the South China Sea and they are in position that makes them capable of striking Chinese military bases and trade routes in the area. So, yes even if it's not outright aggression, it's pretty threatening and could certainly elevate tensions between the two countries.
These new rocket launchers are very close to Bejing, and it is quite possible that Vietnam may end up angering the Chinese goverment by moving them there, especially considering how quick to anger and how quick the Chinese government is to declaring war on any country that has policies they do not agree with.
The region remains unstable even though most military maneuvers are simple test and shows of strength. However, anytime Vietnam shows any military presence in the South China Sea, there are ripples of unrest sent to Beijing. The new rocket launchers have a range that should give any country in the area cause for concern.