Is Beagleboard Black a SoC FPGA ?
I have hard that a system with CPU and Flash is kind of SoC FPGA, Am I right?
No, an FPGA contains programmable logic. Flash is storage. Yes, you can make look up tables in flash that emulate some simple FPGA functions, but flash is not an FPGA.
An example of a SoC FPGA is the Xilinx Zynq. The ZCU104, PYNQ-Z1 or PYNQ-Z2 are examples of boards with this type of SoC.