i don't know, you can make this site with any cms. if i want to make this site, i will use wordpress.
That is custom CMS made through PHP and Mysql. Although, similar thing can be done in wordpress too. Should not be much difficult if one has theme.
it is a custom script. i do not agree that it is a modified drupal though. it can also be a modified WP install. and i cant tell you what the theme is, because that also is most likely custom.
They probably had the the entire site and backend done by a developer instead of using a third party CMS script. Bear in mind that not everyone likes using third party CMS and would rather prefer the same functionality tweaked and customized to their needs, which is what appears to me to be the case with this particular site...