Job role — a SECURITY object. Determines what pages and functions you can reach anywhere in the system. Granted by an administrator, via the Security Console.
Project role — a PROJECT object. Determines your part on a specific project team: project manager, team member, and whatever roles the business defines. Granted by adding you to the project team.
Different objects. Different owners. Different granting mechanism. The same person can be project manager on one project and a team member on another. Their job role does not change; their project role does, per project.
What each controls, as a question. Job role: can you open the project costing work area AT ALL? Project role: on THIS project, can you approve the plan, view financials, edit the schedule?
"PROJECT MANAGER" EXISTS AS BOTH. Some project roles and job roles share names. That is the entire source of the confusion. It is said explicitly because you will hit it, and if nobody warned you, you would conclude you had misunderstood something deeper than you have.
And one thing that makes the project role list a design object rather than a convenience. Rate schedules can be role-based. Resource management staffs assignments by role. So the project role list has more than one consumer, and a list invented casually for team membership turns up in Module 6's pricing and Module 17's staffing. KEEP THE PROJECT ROLE LIST SHORT AND MEANINGFUL.