That location would calculate to be the location 9MMRO would have run out of fuel had it been maintaining a 428kt groundspeed (based on potential flight duration according to known fuel on board.)
That seems to most people to be a unrealistically slow speed, which is why most of the effort has been further SW.
The "ping rings" are based purely on the BTO timing which only requires a fairly simple mathematical calculation to determine the distance 9MMRO was from the satellite at a given time. We should remember that the first ping ring (at 18:29) matched up perfectly with the predicted location of the plane vs Malaysian radar data so I (and many others) have faith that the plane was at the predicted distance from the satellite at the stated times; hence on (near) the 00:19 ping ring at the time it hit the water.
I wish I had as much faith in their side scan radar finding a crumpled fuselage though.