No not technically a flush valve. A flush valve would be on the waste water line. It's used to bypass the flow restrictor to allow a lot of water to flush over the membrane surface and pull waste that has trapped itself on the pores of the membrane, and flush them out the waste line.
This would be a bypass valve to allow RO water to be collected before entering the DI section. Area circled in red, there is a T on the RO line and two valves that allow me to control which direction the RO water flows.
