Clerk Pulls REAL Gun Against Robber's FAKE Gun! Lawful?

An Orange County CA liquor store found himself the victim of an armed robbery recently--but then realized that the robber's gun was not real. The clerk then presented his own real gun from under the counter. The robber, realizing he'd brought a fake gun to a real gunfight, immediately fled. Is it lawful to pull a gun on someone threatening you with what you know to be a fake gun? After all, where's the deadly force threat? Learn the Self-Defense Law you NEED to BE HARD TO CONVICT, for FREE! ...