I'm not sure this is true. You can get basic OO going on C in an afternoon with structs and function pointers. That is a very, very common technique in graphics programming (or was, before C++ optimizers got any good). ObjC is also a thing. The achievement of Stroustrup - and this is no minor thing, so don't think that I am discrediting him in any way - was he got everyone else to buy into his vision for a particular way of doing it.
Incidentally I recently attended a talk given by Stroustrup and he is a super nice guy and certainly doesn't think of himself as a genius.