A 29-year-old female with schizophrenia was previously on risperidone 4 mg daily, which controlled her positive symptoms but caused significant hyperprolactinemia with amenorrhea and galactorrhea. The PMHNP switches her to aripiprazole 15 mg daily. At her 6-week follow-up, her prolactin level has normalized and menses have resumed, yet her positive symptoms remain controlled. Which of the following best explains aripiprazole's unique pharmacological mechanism that accounts for these outcomes?