How is the total area of the world's oceans 361 million sq km?
Commenter Universal Learner points out "Currently NOAA says there is only one ocean"

https://oceanservice.noaa.gov/facts/howmanyoceans.html

and "At the comments of the question I linked you can read a great: "I once heard a lovely description of the world's seas (by a polar scientist) as "One ocean with three big estuaries" ;-) "


  While there is only one global ocean, the vast body of water that
  covers 71 percent of the Earth is geographically divided into distinct
  named regions. The boundaries between these regions have evolved over
  time for a variety of historical, cultural, geographical, and
  scientific reasons.
  
  Historically, there are four named oceans: the Atlantic, Pacific,
  Indian, and Arctic. However, most countries - including the United
  States - now recognize the Southern (Antarctic) as the fifth ocean.
  The Pacific, Atlantic, and Indian are known as the three major oceans.
  
  The Southern Ocean is the 'newest' named ocean. It is recognized by
  the U.S. Board on Geographic Names as the body of water extending from
  the coast of Antarctica to the line of latitude at 60 degrees South.
  The boundaries of this ocean were proposed to the International
  Hydrographic Organization in 2000. However, not all countries agree on
  the proposed boundaries, so this has yet to be ratified by members of
  the IHO. The U.S. is a member of the IHO, represented by the NOS
  Office of Coast Survey.


And they have a graphic saying 1 world ocean.  Historically 4 basins.  Now 5 basins. And that the boundaries aren't agreed upon by all countries. Though that text refers to a basin as an ocean, so their terminology doesn't quite match their graphic.