Things like this are the underlying principles of smart card payment networks. Like Suica in Japan and Oyster in London.

Although this paper uses rather fancy techniques, the general concept is far behind Bitcoin; it is a scheme that merely allows people to prove their balances in banks and sign their transfers, of a centralized currency where the main service nodes (banks) have the final authority of whatever can happen. There are many other people who do this kind of research.

I also took a glance at his publications, and I see that his work is much more delicate than Bitcoin, while none of it resembles any kind of interest in something that could relate to P2P cryptocurrency protocols. I also have a hunch that Okamoto is a better mathematician than Satoshi Nakamoto, comparing Okamoto's papers to "that" bitcoin.pdf.