That document does not support the UN Navy involvement in CENTOM. That is a different mission statement. The US Navy asserts: "The United States is a maritime nation, and the U.S. Navy protects America at sea."
So the question remains. "What was being shipped, from what country and to what country?"
Some answers could be 1) "we are the world's policeman," 2) "we're paying for other nation's ships and cargo when they are not paying," or perhaps 3) perhaps the cargo was "American?" I suspect the last is not the answer.
What seems likely, unless you have citations to suggest this incorrect, is that the "Maersk Hangzhou, a Singapore-flagged, Denmark-owned and -operated container ship" might not be fully funding the protection of their business enterprise.
The article does not mention what the cargo was, nor its origin and destination. If not the US, and if we are funding the large share of the policing, there is a significant imbalance in the world, given the US' $34,000,000,000,000+ national debt.
But the US Coast Guard statement does not address this at all.
The USN mission statement does support freedom of the seas. As a USN veteran, I can assure you that one of the primary missions is keeping the seas open and free.
Mission Statement
The United States is a maritime nation, and the U.S. Navy protects America at sea. Alongside our allies and partners, we defend freedom, preserve economic prosperity, and keep the seas open and free. Our nation is engaged in long-term competition. To defend American interests around the globe, the U.S. Navy must remain prepared to execute our timeless role, as directed by Congress and the President.
https://www.navy.mil/About/Mission/