Windows 10 quality updates explained and the end of delta updates

DTP6144: 
Quality updates refer to the monthly updates that contain quality fixes (security and other bug fixes).  In the site you linked to that explains LCU and SSU terminology you'll see that the person who answered the question was actually incorrect the first time and referred to LCU's as feature updates.  In a later response they clarified and stated that LCU's are quality updates.

The correct answer is more complicated though: LCUs can actually be used for both quality updates and feature updates.  LCU is a way to compress and package component changes together so they can be installed successfully.  The component changes themselves could include bug fixes (quality update) or features (feature update).  The decision to label something a quality update or feature update is a policy decision and isn't limited by the technology that supports the update.

I hope that helps instead of making it even more confusing 🙂