When a Project Hotlinked drawing (data are linked to a View in an ArchiCAD Project) placed in PlotMaker is updated, PlotMaker starts Background ArchiCAD. This copy is started solely for the purpose of regenerating in ArchiCAD the View(s) that need updating in PlotMaker.
On the Mac you can see this copy appearing among the icons at the bottom of the screen. You can switch to it and exit it. Under Windows, it remains invisible to the user.