Actually, the origin of the tension between Motobu and Funakoshi is to be found in Kyoto in 1921. At that time, Motobu was 51 years old and has fought and defeated an European boxer, nationality unknown, some say Russian, Pole or Estonian. At any rate, the guy was way bigger than Motobu but was nevertheless defeated via KO, probably thanks to a punch to the face between the mouth and the nose.
The magazine King (pronouced Kingu in japanese) wrote a couple of years later an article about this very fight and put a picture of Funakoshi instead of a picture of Motobu. Picture under.
This, of course, infuriated Motobu who felt that Funakoshi took the merit for something which he did not do and, according to Motobu could not have done. Hence the reason for Motobu´s visit to Funakoshi and the following "fight/challenge".
The empty hand martial art of the Motobu family was known as Motobu Udun Dii and was a family art transmitted among the Motobu Family but only to the first born son. It is Motobu Choyu and only he who inherited the system from his father as the tradition wanted, this is to say, from father to first born son. Motobu Choki was the third son and was probably not schooled in the family art. Picture of Motobu Choyu under.
In any case, Motobu Choki was famous for picking up fights and even though it is very unlikely that his older brother would have taught him anything, the possibility cannot be totally ruled out. As a matter of fact, though the Motobu Udun Dii, while still practiced, does not belong anymore to the Motobu family but was passed to Uehara Seikichi Sensei who passed away at the beginning of this century at the beautiful age of 100.