This was my initial reaction, but he is talking about a function that happens to be named memcpy() and what the compiler is allowed to do with the provided source code. So you should actually blame him for defining a function with the same name as a standard function (an undefined behavior). What would make his example correct is to use any name other than a reserved one, that is, not "memmove".
If you look more closely, you will also see that his memcopy dereferences a void * (and performs some pointer arithmetic as well). Apologies for my inner pedant getting the better of me.
