The water elves wanted to act cleverly by rescuing their friend and running away without caring what happened to Andrew's group even though they were helping them.
It's not that they are ungrateful, but they are distrustful by nature. Unlike other elven communities, the water elves are small in numbers.
This is why, despite being the rulers of this country, they leave all matters of government and such to the humans. At first, this worked well, but over time the humans had become more numerous, and from there came greed.
Being the most numerous and the ones who control everything, why should they obey the water elves? That is the thinking of many humans in the country currently and they have even gone as far as kidnapping water elves like the group facing Andrew and his wives now was doing.
