Yes that's very weak evidence, and Satoshi Nakamoto is a name used under a pseudonym, and even though it's a Japanese name, it doesn't mean he's Japanese. And maybe he's just someone, maybe they're the people who developed bitcoin or the team, wrote the bitcoin white paper, and created and implemented the original bitcoin reference implementation.
and as a pseudonym, we cannot guarantee that Satoshi Nakmoto is from a particular country and this is very difficult to solve.