https://www3.nhk.or.jp/nhkworld/en/news/20181101_39/
The copilot admitted to airline officials that he had drunk more than 1.5 liters of wine and more than 1.8 liters of beer in a hotel bar and in his room the night before.
That's a good chunk of alcohol to consume the night before. I'm guessing it was spread into the morning to hit that level of intoxication during the test (roughly equivalent of .20BAC). Didn't interact with any other JAL crew until being driven to the plane when the driver of the van noticed? Kind of surprising.