The US helicopters killed the Houthis there, only because the Houthis fired on the US helicopters themselves (who were responding to the Sg flag ship's distress call).
United States Central Command confirmed that helicopters from the nearby US warships Eisenhower and Gravely were responding to a distress call from the Singapore-flagged Maersk Hangzhou, when the Houthi boats fired on the US helicopters.
In response, they returned fire "in self-defence", sinking three of the four small boats and killing the crews onboard.