Indeed – I found this to be a pretty funny statement as well. :)
I wonder if we don’t have a slight confusion in terms here though. I’m going to paraphrase this article, which has information that agrees with what I’ve been told before. There are three terms that are often confused: “cold sores”, “canker sores”, and “fever blisters”. Cold sores and fever blisters are the same thing, and they are caused by herpes simplex. It is unknown what causes canker sores, and approximately 20% of the general population suffers from them.
The easiest way to tell the difference is that cold sores/fever blisters occur on the outside of the mouth, usually around the lips, but can be farther out. Canker sores occur inside the mouth.