@Daisy, I'm not sure how it worked. Adding a comment will not republish the object so it shouldn't trigger that workflow.
@Pascal, AFAIK that's not possible for now. Because eZComments is using a different content model from ezpublish object model. Comment in ezcomments is not a object, so the workflow trigger can not be applied here.
For future, basically there should be a possibility to achieve this by some eZComments enhancements for workflow.