Product Quality focuses on the quality of the “product” of the project. It is measured in terms of the degree to which the product conforms to customer’s requirements.
Whereas, Project Quality focuses on the quality of “project management processes”. It is measured in terms of the degree to which the project meets its objectives (scope, time, cost, quality etc.).
For example, a project that delivers a good quality product (one that meets the customer’s specifications), but exceeds the budget, fails to meet the project quality requirements.