Yes it's factory. Somebody didn't know how to remove the center thinking the faux bolt heads were real and stuck an allen wrench in them to "remove" them.
As you can see in my avatar I had the SS's (circa 1976). Man those things sparkled when they were rolin down the street. I had corrosion problems on my original wheels almost from day one though. Always wondered about the cast center steel rim, galvanic action maybe? Got my second one in 85...