Wong Chong Yoh was a xingyi guy in the 1600's. He taught Chatan Yara, who taught Sakugawa, who taught Matsumura, Shuri-te, the first guy we know of who did naihanchi kata. He may have gotten it from Ason. The form may have also been passed down to Matsumora thru a Tomari-te lineage. Hard to really trace it with certainty, like much of karate history.
The book is Karate Uchina-Di (Ryukyuan dialect for their native hand). Author is Itzik Cohen. According to his bio, a long-time karate-kobudo practitioner and researcher. An Israeli officer in infantry and Directorate of Military Intelligence. This 600-page book gives a very detailed history of Okinawa, its relationship with China and Japan and all the cultural factors that came into play over the centuries. He then ties all this in with the evolution of all aspects of karate and how it came to be. It's like two books in one.
I found this in an article on the internet while searching Ason who was quite influential in the 1800's. I haven't seen this term anywhere else so can't confirm it. The English translation was provided as "fighting on an uneven surface." This kind of makes sense based on the limited footwork.
That's as good as any.