If it was a merchant ship, then WHY did the US demand payment of the price of the ship 20+ years later? If the merchant ship was doing something illegal (which it was by having the Mexican official aboard and running guns), then why would the US side with the merchant?
Very tellling! Imagine if we found ship running guns to IRAN, and the government DEFENDED the merchant!
1. Doing what the ship did was not illegal under US Law. There was no embargo placed on Mexico during that war and no international sanctions placed on them either.
2. The US Government didn't demand payment. It was a civil suit in US maritime court brought by the owners of the ship, not the US Government. They rightly collected in the end because legally they were correct. For the Texans it was a small price to pay for independence. Many war end with compensations negotiated afterwords for 'actions' against 3rd parties taken during the hostilities.
It was all pretty standard maritime law. During that revolution, the Texan revolutionaries had no legal standing anywhere in the world. For both the Mexican government, and under US and international law, that ship was only bringing goods from one Mexican port to another Mexican port.
It was doing nothing illegal under any law and perfectly within its rights, albeit it was doing something very dangerous in the midst of a revolution.
It is not "if' it was a merchant ship. It WAS a merchant ship. Try to understand that there is a big difference between a US flagged vessel and a US Navy war ship.
The initials might help you comprehend this. The SS Good Ship Lollipop that runs day excursions on your local waterway is a "US flagged vessel.", it is a merchant vessel. It operates under US and International maritime law. The USS Ronald Reagan is a US Navy warship!
Two totally different things.