Was Pocahontas traded for copper kettles?

No, what the English called being traded for an object, was the Native American tradition of intermarriage to solidify trading bonds and establish good relations, and future peace. The French took advantage of this tradition, and it's a well known part of French, Metis and Canadian history.

This took place in a time period just a few years before the English thought that going to buy some African human beings, for the intended purpose of generations of slavery, was a fantastic idea. The context of Pocahontas leaving, to live with the English, was warped and distorted through their racist minds. They saw what they wanted to see, which was a savage people who sold their daughters for pots, rather than see a man who made a hard decision to give up his daughter to his enemies, but kept in line with his traditions, for the greater peace of everyone. Little did they realize how incredibly racist the English were, and the intended context and purpose was turned against them.

Native Americans and First Nations were not selling their own family members to the English.