WMI Event Alerts - SQL 2005, what is the excution environment looking for as a return ?

I have started using WMI Event Alerts on SQL Server.
A simple example being :

Namespace :   \\.\root\cimv2

Query:

SELECT * from  __InstanceModificati
onEvent
WITHIN 30
WHERE
TargetInstance ISA 'Win32_Processor'
AND
TargetInstance.LoadPercentage > 80

My Question :
What is SQL server looking for from the query to determine if an alert
needs to be triggered. My interpretation from this simple script is :
If any row count is returned (ie SELECT * from ..) then the alert will
be fired.

Is this correct for all WMI Event Alerts ? Is that all it is ? ie
Rowcount returned > 0 ?

Thanks
s