The first step in understanding Instructional D3 is distinguishing between the tasks performed for the project and the tasks you perform when developing instructional products.
Without going into too much detail, project management involves all aspects of a project, including the tasks required to create the product. This includes the budget, communication management, resource management, quality assurance, risk management, and scope management. The project management tasks focus on who, when, where, and how something gets done.
Product development focuses on what needs to be done. What tasks are performed to yield the instructional product. It is the "what" that drives many of the project management tasks and therefore is a critical part of an instructional product development project.