It seems to me that Mr. Botezatu isn't much of an expert. He cites one "virus", the Flashback malware. It does depend on how technical you want to get with that example.
1) Flashback did indeed behave exactly like a virus in that it infected a computer without any assistance from the user. But, it only worked if you had Java installed, and it was enabled in your web browser. If you didn't have Java installed or enabled, then a loaded site would pop up a message to try and get you to manually agree to install something. Which is Trojan activity. You have to allow it.
2) Flashback was never an OS X virus. It was a Java exploit. So from that technical aspect, OS X itself has still never been infected with a virus.
The KitM.A backdoor he mentions was spread as a link or attachment in an email. So again, not a virus. It's a Trojan you had to download and install.
Rootpipe isn't malware at all, of any kind. It's a long standing flaw in OS X's underlying Unix code that was just fairly recently discovered.
So once again, an "expert" is throwing the words virus and OS X around as if it means something, when they are, once again, wrong.