All the other LP's were also Japanese LP's. Decision was based simply on packaging. This was gatefold, with inserts, including photos of locations/trains/engines. There is no english text is any of these.
I'm not surpriced about good quality of late 60's recordings in some ways, because music / studio recordings of the time of course are often supreme compared to standards of today. But I'm impressed by the task what it must have been to make it, since not talking of easily portable DAT, harddrive recorders etc. with built in mic's.
This differs from the "sound effect" albums, because it is clearly not just sound effect. One can found those movie/radioplay backing effect LP's and CD's basically anywhere. Sounds exists as pieces of documents of sound & location, not for purpose to be used anywhere else (although they can be)? Especially in Japan, there seems to be lots of train enthusiasts. You find several train magazines in shops. I'm sure some of readers prefer to listen this kind of stuff.