Executing plugin on Case Entity though not registered in Child Pipeline

Hi All,
I created a CRM 4.0 plugin on Case Entity. Event: Pre-Event Stage,Parent Pipeline, Message: Create, Synchronous. Plugin is working fine as expected. When I am creating a case from contact also plugin is firing. I was surprised that how it is executing though i didn't register in child pipeline. As per the below url it should not execute since i am creating the case from Contact (as it belongs to Child pipeline). Kindly clarify if my understanding is wrong.

Url: http://crmscape.blogspot.in/2009/02/ms-crm-40-plug-in-stages-pipelines-and.html

Regards,