Answer
No, Al-Husayn ibn al-Qasim was not a ruler of the Abbasid Caliphate. Instead, he was a prominent Zaydi Imam and a great-great-grandson of Hasan ibn Ali, the grandson of the Islamic prophet Muhammad. He led several uprisings against the Abbasid Caliphate, seeking to establish Zaydi rule in Yemen, and even managed to capture the city of Sana'a for a brief period.