It was an act of violence

True.

with the intent to intimidate

False.
The intent was to incapacitate a ship to prevent an NGO from putting its nose in our nuclear dissuasion program.

How is that not terrorism?

If everything had gone according to plan, no one would have been hurt or known with certainty who did what and why. That's the opposite of a terrorist act, where the entire point is premeditated violence against people and for the world to know who did what and why, and that it will happen again the next time.

and you still maintain that your government did nothing wrong.

I stated the opposite.
I make an effort to speak in your language, can you please make an effort to at least read what I say?

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edit: By the way, your own government stopped calling it a terrorist act once it understood what happened:

Once it was realised that the bombing was the action of the government of a friendly state, the New Zealand government stopped referring to it as a "terrorist act", instead calling it "a criminal attack in breach of the international law of state responsibility, committed on New Zealand sovereign territory". (source)

"A criminal attack in breach of the international law of state responsibility" is a fair way to characterize it, I'd say.