The chapter emphasizes that it’s a separate personality system that’s running Harry at that point (which doesn’t prove it’s Voldemort, but is suggestive). E.g.:
that’s not Harry--
You know. About his dark side.
Although it’s not absolutely definitive; Dumbledore’s line in reply is
But this is beyond even that.
which argues for “he’s damaged” as you suggest rather than “he’s alien [and Voldemort]” as I’m suggesting.
I believe Dementor!Harry was just damaged by the Dementor, producing both grotesquely negative motivations and poor impulse control.
The chapter emphasizes that it’s a separate personality system that’s running Harry at that point (which doesn’t prove it’s Voldemort, but is suggestive). E.g.:
Although it’s not absolutely definitive; Dumbledore’s line in reply is
which argues for “he’s damaged” as you suggest rather than “he’s alien [and Voldemort]” as I’m suggesting.