The board uses a Freedom E310 RISC-V microcontroller. The PCB size and connector layout is the same as an Arduino, and also there is some software-compatibility with Arduino's programming environment. But it's definitely not ARM based.
What makes this so interesting is that the instruction-set (RISC-V) is free for anybody to implement, and has growing academic support.
The E310's RTL source-code is also open-source and freely available, which means you could implement your own version on an FPGA or approach a chip-fab if you wanted to build a lot of them.