The article doesn't state that the improvements stem only from the iPhone 5, rather that since the iPhone's launch in 2007 the addition of the security features listed in the third par have led to the perception among IT directors that the iPhone can match BlackBerry handsets for security.
That perception that iPhone can provide good enough security for many workplaces is backed up by the assessment by the security vendor Trend Micro referenced in the article - see: http://www.trendmicro.es/media/wp/ent-readiness-mobile-platforms-whitepaper-en.pdf
What IT directors think matters as they are they have sway over whether iPhones can be used to access work systems.