There is something like a 90% return rate on lost wallets in Japan. Failure to attempt to return a lost item of value is an actual crime... so if the bag was not sitting on the street next to him when he woke up and not returned by a kind soul it was by Japanese definition stolen

Edit: An eye opening video on how well this works https://www3.nhk.or.jp/nhkworld/en/ondemand/video/9999897/