HuffPost has an article that links to a PDF of the DOD Law of War Manual. You'll find the link at the end of the 2nd paragraph of the story. Click on "reads". The instructions about how to treat enemy combatants that the Navy has shipwrecked begins at Section 7.3 on page 448 of the Manual (page 476 of the PDF file).
The manual is unambiguous about not killing shipwrecked people, including enemy combatants. They are to be rescued and kept in custody as POWs.
It's important to understand this is not the Uniform Code of Military Justice. This is, in effect, published legal advice from the top counsel at the Pentagon.
It is also worth reading the Foreword.
From this manual, it is clear that the second strike on the Venezuelan boat was unjustified. This isn't about violating international treaties; it is a violation of our own laws of warfare. Illegal orders. Admiral Bradley is a four-star officer. He would be expected to know this. So, he either issued or obeyed an illegal order.
Hegseth is the one in trouble here. You can tell because the two stories being peddled are that the order came from Trump or from Bradley. Both stories protect Hegseth, which leads me to believe he gave the order.