Metabunk explained this one months ago, and even identified the aircraft involved. The useful fact that the dtailed flightpaths of all airliners are recorded and logged in a database nowadays allowed them to look back and see exactly which plane was in the frame for this one. I expect every encounter could be explained in this way (or in other, related ways), given enough data.
Lots of unsatisfactory aspects to this case. The pilot has seen UFOs before, which always makes you wonder if he is just a 'serial reporter' who thinks anything in the sky he can't immediately explain is an extraterrestrial. The other two flight crew apparently did not see the same things as he did, possibly because they were sitting on the wrong side of the plane, or maybe they were just more level-headed.
And the final aspect of the sighting was a huge, black craft as big as an aircraft carrier, that his crew could not see. The thing about this is, well,
... the thing about space, the colour of space, your basic space colour, is black. and the basic colour of this massive object, the main distinguishing feature, that was black too. Basically Captain Terauchi was looking at a black spaceship against a black sky, that no-one else could see, despite the fact that 2 other aircraft had been diverted to take a look.
The radar returns have been adequately explained too, but of course no-one in the UFO camp believes that.