Korean insisting that yakiniku＝Japanese grilled meat is originated in Korea is the usual lie from Korean vanity.
There are culture of grilling meat everywhere, and it was in Japan that the delicious sauce was developed, and with the development of restaurant arrangements and sauces in Japan, Korean food that originally did not tasty at all became delicious in Japanese restaurants.
And Korean origins began to use it in Korean restaurant in Japan and later, spreaded them in Korea, Copied and generalized in there.
And in the last 15 years or so, all Japanese yakiniku has started to be translated into English with "Korean grilled beef" always even for Japanese in-flight meals in airplane, which is really annoying.
But I got used to such things and not mind this so much now. Because they have been doing far more similar terrible acts than this yakiniku matter,