How is it that Iblīs is given as an exception from the angels (by the apparent wording)?

Imām Ibn al-Jawzī (d. 597/1201) summarized the scholars' opinions in his book "Zād al-Masīr" as follows:

1. It is an exception from the same category (of beings), meaning that Iblīs is from the angels. [Ibn ʿAbbās, one narration from Ibn Masʿūd] It has been also narrated from Ibn ʿAbbās that he was originally from the angels, but then Allah transformed him into a devil.
2. It is an exception from a different category, since Iblīs was from the jinn. [Al-Ḥasan, al-Zuhrī] Ibn ʿAbbās states: Iblīs was from the guardians of Jannah, and he was responsible for managing the affairs of the Heaven (al-samāʾ). (Ed: hence Iblīs was among the angels but not one of them.)

One might ask: How can a grammatical exception be applied to him when he is not part of the same category (as the angels)? The answer is that he was commanded to prostrate along with them, so the exception was made because he did not prostrate. This is similar to saying: “I commanded my servant and my brothers, and they obeyed me—except my servant.” [Al-Zajjāj]