
The Houthi’s are enforcing their ban on ships headed to or from Israel to enter Yemen’s water territory. They did this as a sanction on Israel because Israel is committing genocide on the Palestinian people. When the US and European countries started bombing Yemen for enforcing their law, they also banned US and some European ships from entering their waters. During the ceasefire they lifted the blockade, and since Israel ended the ceasefire they started banning ships again.
With US track record a majority if not all of those 53 people were civilians