It says they did not have their Japanese driver's licenses. Maybe they had obtained an International Driver's License before arriving in the U.S.
From your link:
Our IDD is an unofficial translation of your Driver’s License in two formats: A Translation Card, translating your permit in 16 languages, and a Translation Booklet, translating your Driver’s License in 9 languages. These unofficial documents will help you overcome language differences when traveling. As a complementary feature, our advanced translation card saves a digital copy of your valid Driving Permit in your Smartphone!... Amazing.
International driving permits, which are booklets issued by governmental agencies or private organizations designated by a country’s government, are the only official translation of a person’s driver’s license. Our translation has no official status and does not confer any legal privileges or rights on consumers.
So all it is, is a translation of your drivers license so that a foreign cop can understand the info on your home county license. You must have your home country license to accompany the IDL.
And this thread reminds me, I need to go get one. Going to France in May.