It’s real that they detained a cargo ship, but it is a Maersk ship, which is either Danish or Swedish.
Which brings up a question as to why a Saudi press outlet would announce seemingly definitively that the ship is US. They have a strong interest in having somebody, the US, Israel, somebody cut Iran down to size. I believe that interest in this case parallels our own but we still don’t want to be the dog wagged by a Saudi tail.