As a native Japanese, I can tell you that is true. There are many types of Japanese paintings, but the most popular is ukiyo-e. And I can't think of a more famous ukiyo-e work than "Great Wave". Therefore this is considered the most famous Japanese painting.

If asked to choose one ukiyo-e as an illustration for a banknote, almost all Japanese would choose this work. (Especially considering that the back of the banknote, i.e., a landscape, is required)

Although less famous than "Great Wave", however there are still works that are comparable to it. "Yakko Edobei" by Sharaku is one of them, and it's the most famous ukiyo-e portrait work.