Well, software failures in the medical field are unlikely to be caused by security holes... that's his point actually, even though it is a field which isn't suited for Linux.
Actually it is, i do some contract work for a huge biotech company who use a suse-based linux system for monitor & control of machinery, which has something to do with manufacture for protein separation for the hospital nearby. Its highly specialized stuff which is probably why they use it (they have re-written it and customized it to do the job) its highly stable and dedicated to the task. A system crash in there would be either very dangerous or very expensive which is why they need a rock solid system. Some of the main servers are also suse, aix or solaris.
Needless to say us 'windows techs' are not allowed near it. :)
while by telling that security holes are as important as any other bug he is actually confirming the fact that there aren't many viruses on Linux just because it isn't widely used as a desktop environment.
While thats probably partly true, and there are viruses for every OS, it is much more difficult to write actual exploits and spyware on a linux system simply from the way it is built and operates. Most of the few linux/unix viruses work badly or not at all because of this. Still there is no defence against admin/root-user stupidity though (on any system!)