Was Nabeel Qureshi a Muslim?

Nabeel Qureshi was raised in the Ahmadiyya sect of Islam. He attended a Sunni mosque, prayed the required daily prayers, and fasted during the month of Ramadan. Eventually, Nabeel left Islam and became a Christian. Many Muslim apologists now tell their fellow Muslims to dismiss Nabeel's arguments because he "wasn't really a Muslim." Is this correct? In this video, I answer three questions:

(1) What are the beliefs and practices that qualify someone as a Muslim?
(2) What did Nabeel Qureshi believe and practice before he became a Christian?
(3) Do Ahmadi beliefs and practices rule one out as a Muslim?