As far as I know, there is no leader in the bitcoin world. It is decentralized, there are no leader to control the bitcoin. How can I think or determine that Japan is the leader, what will be the basis to become the leader. To become a leader that leader must command and control an organization.
Maybe hes pertaining on the ranking on countries which do accept or legalize bitcoin. We do know that Japan is the first country as far as i know who do legalize bitcoin and adopt it to be part of their payment system which we cant see on any country.They did really do such thing knowing that satoshi is a japanese maybe this is one of the factors why they do legalize it but well this is just my own opinion.