To me it seems that Risc-V is China's 'plan-B', their systems are the first to use it and SBC's do exist already in China. I've even seen IoT cores from Chinese vendors moving to Risc-V, like the popular ESP32 from Shanghai company Espressif.
AFAIK Allwinner is a Chinese company and the C906 core is an open source core made by Alibaba.
AFAIK C906 is not open-source.
The open-source variant of C906 is called OpenC906, and we don't know the eventual difference between C906 and OpenC906.
Even if the C906 and OpenC906 were the same there would be no way to verify that the cores implemented in the hardware you receive are the same as those described anyway.