Is not Iblis one of the jinn, so how can he be of the angels?

Iblis is from the jinn, according to the clear text of the Quran. He was created from fire and has offspring, unlike the angels, who were created from light and do not procreate. The exception of Iblis in the verse: (And [mention] when We said to the angels, "Prostrate to Adam"; so they prostrated, except for Iblis) is a disjunctive exception, meaning that he is not of the same kind as the angels; rather, he refused to prostrate.