The tsunami warning was canceled soon after being issued.
There are essentially 2 kinds of earthquakes:
1) A quake caused by the horizontal movement of 2 plates against each other.
2) A quake in which one plate is suddenly uplifted.
It is this second one which causes large tsunamis. There is also no way to tell, at this time, which kind of quake is happening. The effects of either quake will be the same, in terms of strength, but the effect of one kind of quake is quite different from the other, in regard to its potential to create a tsunami.
In the end, it is better to be safe than sorry, and I am glad that this was not an event in which a plate was uplifted.
More on the South Pacific quakes here.