The text fails to mention that Freud started out studying physiology and neuroanatomy. His early knowledge of physiology let him to believe internal states were really physiological. But he was frustrated with the technology of the time. PET scans and such weren't available for him to observe the physical and chemical mechanisms underlying behavior. He created theoretical constructs on purpose as metaphors for what happens in the mind.
Psychoanalytic theory appears to be dualistic.
Freud said that these people had desires, urges, and wishes that they weren't aware of. He said these were part of the 'unconscious' mind. These urges could be very basic but could lead to complex and strange behavior. This might be because he has a secret sexual urge and his unconscious is making him go towards books labeled 'S' for Sex. So he kicks his younger brother instead.