Zein did not really expect to get a vision from this fragment.
From the twelve fragments they got in the war, Zein did not receive anything significant. Some had no vision at all--perhaps erased during the subduing process by the shard. But even those with vision only showed him the preparation for the war. In short, it was just new memories that brought nothing to the table. Zein felt like those fragments were new ones made just for that war.
And so, he did not think much when he decided to destroy the fragment right away. Maybe because everything had been easy, he unknowingly became too relaxed and complacent.
That being said, this vision was also a new memory.
What Zein first saw was the sea. But wait, he could recognize it as the sea? Belatedly, Zein realized the place wasn't as dark as the usual Deathzone.
Yes. Because there was a shard there.