This is patent nonsense. The 'San people' are an abstraction created by Western Anthropologists. They are not a coherent culture, nor do we have any way of deciding they are 'one of the oldest'. We have no records of them prior to the Portuguese and Dutch coming to the Cape in the 16th and 17th centuries. This is merely an assumption based on the fact that the same 'people' lived in the area that long ago - whether there is cultural continuation, we have no way of knowing. Based on glyphs and so, there is not enough differentiation to decide continuance either.
Further, the San are hardly peaceful, either today or historically. Read this just the other day:
Trauma and violence in the Later Stone Age of southern Africa | Morris | South African Medical Journal
On the Han Chinese, this is even more erroneous. Firstly, the very fact they are 'Han' shows their genesis in the Han Dynasty from about 2000 years ago. They area similar grouping to the Romans, a small group that took over a large cultural area and whose name came to designate the whole. In like manner, Greeks used to call themselves Rhomaioi or Romans, up till the Greek War of Independance in the 19th century. Chinese history is very violent, with multiple dynasties like the Chin, Southern and Northern Song, Kin, etc. with periods of disunity. To assume they are not so violent is nonsense - they buried people alive in construction, they made large and continuous incursions into the Steppe and Takla Makan, not to mention periods of civil war and disunity. They had reached natural limits of extension on the Tibetan Plateau, the Jungles of Indochina and the cold steppe and deserts of central Asia. There was just a haughty culture of the Middle Kingdom, and lack of incentive to expand - a similar situation to 2nd century Rome say, that also stopped expanding. There was no new technology or crises to drive further expansion overseas or so, either.
Further Chinese Civilisation is 2000 odd years old, but that is not representing a period of limited change at all. The Jewish culture is very conservative, maintaining their calender and Hebrew and such. The difference between the Chinese in the Tang that welcomed Nestorian Christians and Manichees while supporting Taoists vs the Nationalistic Ming, are stark. Chinese civilisation was a dynamic changing entity, about as different between epochs as an Englishman of Anglo-Saxon times was from a 19th century Imperialist, though both still on the same cultural continuum. The Jews by contrast, have maintained a cultural cohesion and conservatism that almost beggars belief by comparison. We are just ignorant of differences in Chinese periods, so we lump it all together; and the cachet of the 'Inscrutable Orient of Ancient Lineage' is a potent myth the Chinese aren't ashamed to assume.