Mas Oyama may have been badass but he wasn't a good historian
Mas Oyama's work was mainly an attempt to prove that JJJ had the longest lineage of any martial art. I tend to disagree with it because it is predicated on the hypothesis of a single origin point for maritial arts and I don't subscribe to this hypothesis.
The two single origin theories are both derived from the Oyama work. One is that martial arts were invented in Africa, traveled to India and were then propagated to China by Bodidharma. The second is that martial arts were invented in Greece, traveled to India with Alexander the Great and were then propagated into China.
The Alexander the Great theory is laughable. There was already quite effective fighters in Afghanistan and India when Alexander got there. If there were not he probably would have kept on going until he had conquered the whole of Asia. Alexander is just too late to really matter and with the mountains and arid plains of Iran and Afghanistan there was little contact between the civilizations of Europe and Asia major prior to him (there was plenty of contact between the persian empire, other middle eastern cultures and Europe).
There were likely Africans in India long before Alexander. However the African origin of CMA (or for that matter the Indian origin of CMA) theories both are predicated on assigning Bodidharma as the founder of Chinese Martial Arts. This is despite the fact that there was wrestling in Mongolia about 2500 years prior to that. Also there are several Han Chinese martial arts which do not hold Shaolin Temple as their point of origin and which probably predated the temple (in some form). You also have to consider that part of the reason that Shaolin became the "origin" point for so many martial arts is because it became a place where martial artists congregated and traded techniques. Many martial artists who had been educated in "non-shaolin" styles would, after a stint in the temple, emerge with a new form. And since they were often Shaolin monks or disciples these forms would be labled as Shaolin.
In addition Kalariapayattu and traditional Shaolin Five Animal Gong Fu (one of the most significant of the "Shaolin" styles and the one that was the basis of many southern Gong Fu styles such as Wing Chun and Hung Gar) are quite different in appearance and technique. Now this is less important since Bodidharma was a couple thousand years ago and there has been plenty of time for divergence, no martial art remains static for even 100 years let alone 1000, but it still does not bode well for Oyama's theory.
I am sorry that this diverges a bit off-topic from talking about JHR, 51 blocks or whatever other name these underground prison styles go by but this particular piece of historical misinformation is one that always bothers me and it has become increasingly popular of late despite the fact that there is no solid evidence to support it.