That is not enough context to discern the truth. When the former confederate states voted to ratify the 13th amendment, is there any reasonable person who would believe this actually constituted the will of the people of those states rather than a coerced position?
We know military guns forced them to "ratify" that amendment, and we also know that it was simply the will of the power in Washington that they do so, not real consent.
So how do we know what sort of pressure was brought on this captain? If he thought they constituted piracy at the time he did them, then why did he do them?
Sounds like a coerced confession, which again, makes it the desired propaganda of the winners.
Amply demonstrating once again that you haven’t a clue what you’re talking about.