Nobody argued that. OTOH, they had no direct contact with Chinese Confucian scholars either, but it would be ridiculous to try and argue that they were not influenced strongly and clearly by Confucianism.
Hiroshi Tada makes a relevant comment at the bottom of the interview here
Of course nobody argued that! Confucian influence was so pervasive in all areas of Japanese culture, for centuries, that you aren't arguing anything either.
It is like you are saying that the reason why Spanish fencing styles of the 1600s were so much more advanced than italian or German was because they maintained ancient Assyrian traditions, and this must be abundantly clear because Jesus was a Jew.