Who is Agile Project Manager?
There is no such designation prescribed in any of the frameworks. PMI is using this term because they understand it is not necessary that a person who is working as a Manager, can't use Agile values and principles. Designation wise they could be a manager, but if their mindset is moving towards and working to realize Agile values and principle, they are agile.
Also, many times parts of the project are executed in a predictive manner, and some part is managed in an Agile way where uncertainty level is high and in this way Project Manager is an Agile Project Manager but this is not a formal designation in any of the Agile Framework.