The code in the article is just a plaything, a C programmer wouldn't use any of that and wouldn't use C++ as a starting point for their C implementation. Don't let it reflect negatively on C.
In what way? I have seen several examples of C programs that implemented a form of interfaces using structs of function pointers. The GIMP code base does it, as does the Linux kernel's Virtual File System layer. This is a good overview: https://www.kernel.org/doc/Documentation/filesystems/vfs.txt
