Wa alaikum salam. No, Satan is a djinn.
And [mention] when We said to the angels, "Prostrate to Adam," and they prostrated, except for Iblees. He was of the jinn and departed from the command of his Lord. Then will you take him and his descendants as allies other than Me while they are enemies to you? Wretched it is for the wrongdoers as an exchange. (Surat Al-Kahf 18/50)
Angels don't have free will, thus are not capable to antagonise (resist) Allah's orders. They have to obey by their nature. Djinn and Mankind have free will and choice.
Angels are created from light, while djinns are created from smokeless fire.
And He created the jinn from a smokeless flame of fire. (Surat Ar-Raĥmān 55/15)
[ Allah ] said, "What prevented you from prostrating when I commanded you?" [Satan] said, "I am better than him. You created me from fire and created him from clay." (Surat Al-'A`rāf 7/12)
For example there is a class with 30 students. 28 of them are very successful and 2 of them are just average. If you claim that this class is successful, would it wrong? This is called generalization.
Lets say you are a teacher and the class has 30 students. They are not listening to you, if 29 of them are male and just 1 is female, if you shout them as "Guys, listen to me!", does this sentence give the permission to talk to the female one?
My point is, this is not a mistake, it just a way of talk. Its more like Allah says in some verses "We did...". There is no multiple gods and Allah points in that sentence to himself (not he, but whatever). As in this sentence Allah uses "royal we (meaning me)", in your question he uses generalization. In that moment, there are probably thousands (maybe millions) of angels and there is 1 djinn. Should Allah say "I said to the angels and Iblees, ..."? He might had, but this way is not a mistake.
By the way, apart from all of this, when Iblees didn't prostrate, Allah asked for the reason. This means, he is expected to follow this order. Furthermore, he didn't replied as "I am not an angel, so I didn't realize that I should prostrate too." But, in Surat Al-Kahf 18/50, it is very clear that he is not an angel, but a djinn.