Generally when I’m idly visualising something it is ‘in my mind’s eye’ as you put it. But if I’m really focused and close my eyes then everything else seems to disappear and I’m ‘really’ seeing it, not on the inside of my eyelids but it encompasses my entire visual perception if that makes sense

More rarely I also get it with sounds and then it definitely does feel that the sound is originating externally to my mind

You’re right that these experiences are more like hallucinations but I think they are points on a spectrum rather than separate things