Citation needed. My entire family has Macs, and I have never seen this. As far as I know it is impossible to add toolbars to Safari: there is no API for doing so.
What do you mean by "citation needed"? I highly doubt the parent poster documented the event. It is not impossible to add toolbars to Safari (e.g. http://blog.gregfiumara.com/archives/134)
Just because it hasn't happened to you, doesn't mean it never happens.