The phishing *sites* were predominantly on Linux - not a great testimony to security, but then a lot of people with no *nix admin experience put up an internet connected server and do nothing about hardening the OS or even installing the latest patches. A fresh Linux install is generally no more secure than Windows (depending on the distribution). It does suggest the phishers know a good web server when they see one

However the article did not disclose the OS used by the botnet machines, but I suspect the botnets themselves were Windows machines. (Stop press: http://www.theinquirer.net/gb/inquirer/news/2007/10/05/linux-boxes-power-windows confirms this)