@
AbuHajaar They are still separate by the ocean and crossing it at that time period is no easy task along with China's policy at that time didn't allow sharing their knowledge with outsiders and Japan's own policy of preserving their culture and refusing anything foreign, in fact, Nobunaga was one of the first people had an opened mind when it came to foreign things and people at that time period called him a fool and crazy for that .
My country is next to China but in the past, things like embroidery techniques and maize were forbidden to share so some of my country's men had to secretly learn and took them. And if you research, Japanese weapons are really different from Chinese weapons including the bow. Japanese bow called "yumi" is really different from western bow and Chinese's bow in both appearance and the way to shoot.