When I create printer job with PrinterJob.createPrinterJob() it still uses a default printer to print. However printer job settings will have the printer that was passed as a parameter.
To reproduce:
Run attached project
From combobox select printer different from your default one. Do it once. This is important because second time it will not create job, but simply will set another printer to existing one
Click "Print". It will print it's printer from job settings to the console.
Check which it used for real. This will be default printer.