I had the same reaction and question myself. Please tell me if I'm misunderstanding the IBS diet but while there are some similarities, sugars and carbs seem to be the biggest difference. Heather's EFI diet promotes and encourages (or states that they are safe) bread and sugar while the Candida diet calls for elimination.
And I want to throw in that this seems to have turned into a debate over what should be classified as or constitutes an IBS diagnoses. We all know that (some? most?) doctors use its ambiguity to their advantage and simply use it to diagnose anyone with any GI issue. Most of us go straight to work looking for answers and our research leads us to the million and one possible causes for our symptoms. Personally, if I could find a way to resolve my issues, that's all I would care about and not what it's called.