This is true, he was supposedly the grandson of Matsumura Sokon, not his son. There are many karate sensei on Okinawa that kept their knowledge of karate, or the fact that they trained a secret. Either out of the need for safety, or not wanting to be bothered by others wanting to learn. Karate is a very personal thing. And during that time period, at least before the start of the 20th century, it was not allowed to be an openly taught or studied art. Many kept their training a secret. Funakoshi spoke of this in his book 'Karate do my way of life'. When Okinawa was taken over by the Japanese, they did not encourage the practice of such indigenous martial arts, or civil fighting traditions. Especially those of Chinese origin. And outlawed the practice of them. It was later when the Japanese saw value in such arts like karate that it was allowed to be openly practiced. Also in many cases the karate pracitioners of the time kept their practice secret because they did not want others to learn their secrets. Especially the ruling Samurai. I have read that they could have been killed by the samurai if it were found out that they were practicing martial arts.
To this end is why I believe that most if not all kata have so many hidden elements, not easily seen by the novice or layman. What are your thoughts?
I don't think it's accurate to say that before the start of the 20th century karate had to be practiced secretly. I think it is largely a myth, that martial arts were not allowed to be taught openly. Okinawa was invaded by Satsuma clan in 1609. If there was any time that martial arts practice would have been restricted by "samurai", it would have been shortly after this time. Also, during this period Okinawa retained quite a bit of autonomy in order that it might continue its profitable trade with China (which would not trade directly with Japan, officially). It is doubtful that there were any strictly enforced rules about practicing martial arts, since the policing and rule of the Okinawan population was left largely up to the Okinawans.
Another period when the legend about martial arts being banned came from the time when Okinawa was first unified by one king, Shoshin, around 1477. After gaining supremacy and making his capital in Shuri, he ordered all the nobility to move to Shuri, and confiscated all their weapons. Some say it was not even really a confiscation, but that he was just building an armory. But these events turned into the rumor/legend that Okinawans were not allowed to practice martial arts openly, and had to use farm tools to defend themselves. There is no indication that most weapons, and certainly not empty handed fighting methods, were ever actually "outlawed" to the point were people had to keep karate a secret. Additionally, these events took place a couple hundred years before any of the traditions we now know as karate were even developed. Sakugawa, Matsumura's teacher, wasn't even born until 1733(at the earliest), well into the Japanese rule over Okinawa. He didn't start teaching the Chinese martial arts he had learned from Kusanku until 1762. Matsumura Sokon wasn't born until 1798 (at the earliest). He was supposedly a bodyguard for the king, of high class, I doubt his martial arts practice had to be conducted secretly, let alone the practice of subsequent generations of hs family. It is largely from the teachers of Matsumura Sokon's generation that all the shorin ryu kata we have now were passed down, from shuri and tomari. Again, certainly all the kata we have today, in their present forms, were created well after the time when there was any chance of karate practice being restricted.
I believe the reason kata have "hidden" elements is because nobody had taught the applications of the techniques for so long (probably starting around the early 20th century), and kata got changed over the years by people who didn't know all the applications. It is also possible that some teachers didn't want their best techniques revealed too soon, or stolen by people watching them. I'm sure it is true that there are many teachers of karate that we've never heard of, and many excellent martial artists as well. Not everyone had a big school with lots of students. There are family traditions we probably have never and will never hear about, and teachers who do not want to be heard of, or have lots of students. But it's not because there was a law banning martial arts practice, or anything similar causing people to have to hide. The stories of clandestine karate men meeting secretly at night on the beaches, to train with empty hands and farm tools in order to fight samurai are fairy tales.