Why do we say 'Peace be upon him' referring to Angel Gabriel; he's not a Prophet?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions. Jibrail (Gabriel) is also a Prophet (Sallallahu Alaihi wa Sallam) and Messenger of Allah. Allah used to send him to the Prophets and Messengers (Alaihim al-Salaam) of Allah who were sent to mankind. He is the one who used to bring the Words of Allah Subhanahu Wa Tala to the Prophets. The Prophethood is not peculiar to human beings. Allah Says (interpretation of meaning): {Allâh chooses Messengers from angels and from men….}[22:75]. Therefore, saying peace be upon him, when Jibrail is mentioned, is also correct. In fact, invoking blessings for angels, and all believers who are not Prophets is permissible in general, but invoking that for a specific person is dislikeable. In this regard Imam Ibn al-Qayyim said: It is better to invoke blessings upon Prophets, angels, wives of the Prophet (Sallallahu Alaihi wa Sallam), his family and descendents and upon all obedient person in general. But to single out a person other than the Prophets to invoke blessing upon him is dislikeable, particularly if invoking blessings becomes as an identification of him. And also such blessings are not used for the one who is in the same positions or even above his position as practiced by Rafidah . Meaning, invoking blessings only when Ali bin Abi Talib (Radiya Allahu Anhu) is mentioned and not doing so with the other companions of the Prophet (Sallallahu Alaihi wa Sallam). Allah knows best.