Maybe the confusion in the USA is because they think the license to drive a boat makes them a "Captain"?
What does the actual license say?
In the rest of the world the word 'captain' is never used in the license to drive a boat.
I've just checked the net and in the USA there is no such thing, that I can find, that makes one a Captain.
The most common is the 6-pack license:
Uninspected Passenger Vessel
Generally, operations that carry 6 or fewer passengers for hire are referred to as Uninspected Passenger Vessels (UPV), 6 Passenger (pax), or 6 Pack operations. .... the vessel operator must hold an Operator Uninspected Passenger Vessel (OUPV) license issued by the Coast Guard.
So that person is not a Captain, merely a vessel Operator
If there is another type of license often used then lets have a look at it
I see how there can be misrepresentation when websites doing the exam call it a captains license: