To be honest, I think it's fairer to compare Japanese to other Asians. When you do, you will notice that for Asians, the Japanese really, really do dominate distance running.
Compare Japan to all other Asian countries using the IAAF all-time lists. Now ignore Bahrain and Qatar because those are countries importing top African talent.
Hardly any other country shows up! Japan makes up only a small fraction of Asia's population.
So where are all the Chinese, Indians, Indonesians, Filipinos, Pakistanis, etc. who make up most of Asia's population? In Asia, success at distance running is pretty much monopolized by the Japanese. They are the Kenyans of Asia.
Look at these lists. Japanese domination all the way, with a smattering of Chinese, Mongolians, and Koreans.
And yes, Japan also dominates the 5k and 10k track events in Asia.