Final answer:
The Product Increment is not just the sum of the product backlog items completed in the past sprint; it includes all work done from previous sprints as well, thus the statement is false.
Step-by-step explanation:
The statement that the Product Increment is the sum of all the product backlog items completed in the past sprint only is false. The Product Increment refers to the sum of all the product backlog items completed during the current sprint and all previous sprints up to that point. It encompasses all the work that has been delivered since the start of the project, creating a cumulative functionality.