They aren't using fatal error in it's correct sense. A fatal error is an error which a thread/process/application cannot recover from and so crashes to an error. It has nothing to do with frequency but probably will have a common factor, either in data accessed or app. in use, circumstances leading up to etc.
What they mean is that they don't see it as service affecting unless you see it lots.
They are right in that it could have been arrived at through a fluke set of circumstances, if you consistently see it then look for a pattern and consider a backup, then device wipe and selective barebones reinstall. If you're still seeing it I'd redo the O/S and restore everything.
These things were sent to try us ;)