My reading of these articles by Le News and Le Journal is that the change applies solely to travelers from Metropolitan France to the majority of French Overseas Territories, including St Martin and St Barth, and to travelers between the islands of the French Antilles.
I also read them as saying that no testing is required for travel between St Martin and St Barth, but it is recommended that inter-island travelers get either a PCR or Antigen test if they are staying longer than 3 days. Based on the context of the entire articles, I take this as referring to residents visiting the other island, and not to in-transit passengers who might be taking the Voyager ferry.
I read nothing in there which applies to travelers coming from the US.