Yeah, it is very interesting but so true. What a coincidence! Recently I've just watched a Youtube video
where that Chinese teacher told the same story about Prince Shōtoku. At first the Japanese envoy sent a letter to the Sui emperor, claiming "From the sovereign of the land of the rising sun to the sovereign of the land of the setting sun'. The Sui emperor was very angry. And the second time the Japanese envoy sent a letter saying "From the eastern Heaven Emperor to the western Emperor", so Sui emperor became more angry. How dare you say that？It is because Chinese Emperor was regarded as 天子/the Son of Heaven, whereas Japanese Emperor was called 天皇/ Heaven Emperor. Do you try to be my father？Sheer nonsense! Go back!

According to that Chinese teacher, the historical status of Prince Shōtoku in Japan is similar to the Confucius in China. Very honorable and influential!

And he also said that China and Japan didn't begin to establish diplomatic ties officially until Tang dynasty. In Chinese history, Sui dynasty is a short-term dynasty being replaced by Tang dynasty soon later.