This doesn’t do that. It runs an FPGA-built 6502 with 64kB of RAM at 100MHz. The FPGA knows which memory addresses it has to read and write to the actual memory

This doesn’t do that. It runs an FPGA-built 6502 with 64kB of RAM at 100MHz. The FPGA knows which memory addresses it has to read and write to the actual memory of the system it’s plugged in, and, when needed, accesses that at the speed the system expects.