What's your source for this? Say more. As a student of one of his students, I want to know more.
I am not Alex, but I can give some answer.
Yamaguchi Sensei regularly visited Hiroshima and I once asked him where he learned his sword, which sword school he attended. He answered that he did not attend any school. He watched others and 'stole' their knowledge. One of these others was most certainly Inaba Minoru of the Shiseikan Dojo at the Meiji Shrine. Mr Inaba trained at the Aikikai Hombu and was taught by Yamaguchi Sensei and he also trained for a while with Kunii Zenya of Kashima Shinryu. Inaba-shi also trained at Yamaguchi Sensei's private dojo on the recommendation of one Shimada Kazushige. Two others known to me also trained under Yamaguchi Sensei's tutelage and also practised the type of swordwork Alex refers to. One is Christian Tissier and the other was M Sekiya, who lived in the UK for a while.