int and pointer to int are two different types. Pointer-to-int being an option type does not make int an option type. So there are still option types and non-option types.
(Using the prevailing terminology. I'm not sure I'm comfortable with this use of the term "option type", but I'm rolling with it for now.)
Precisely. It's not the case that "any type can be an option type" as shock-value stated. Rather, in C, all pointer types are option types whether you want them to be or not, and all other types are not.
However, 'int *' is inherently "pointer to int or nothing" (in the same style as your NSString example), so I'm not sure I agree with your assertion that some types are option types while some aren't in C. Any type can be an option type (in your sense of the term, again a la your NSString example) by making it into a pointer.
Similarly, using an NSString without a pointer (which might not be possible in ObjC, but definitely possible for regular C/C++ objects) makes it not optional, like the 'int'.