Drupal is a blog and site management software package. Presumably they do their website in Drupal, but so far as I know the normal web user should never get a message like that when simply going to the main web address. Lots of sites are in Drupal nowadays, but you shouldn’t have to install anything to see them..... (so far as I know). [I’m no techie but I know a few techies, fwiw.......]
Ping!