The "GoogleFileTypes" metric was initially created to get a return of code files. I quickly realized that it was returning dynamic content, and so it sort of morphed it into that. (Notice the .h/.c/cpp filetypes are not present.)

I suspect that ".cgi" files are mostly Perl files, but obviously, there is no way to be sure. I'll try and update the metric's description to disclaim this more clearly. Thanks.

Update: I went ahead and removed this metric. It seemed too problematic, upon further reflection.