The proper reason why it cannot be LaTeX is that the file starts with typesettable letters (int), and LaTeX doesn't allow typesettable letters before \begin{document}. Actually it is plain TeX.

What has changed since 2005: rot13-encryption of the plain TeX part (so it is no longer obvious which poem it prints), and the long initial string of the C/C++ part is made more compact, especially the #define q line.