You are correct he is not a man but he was not an angel/messenger. He was the anointed cherub and was adorned with jewels very similar to the high priests urim and thummim.
If being adorned as a priest who was he a priest for?
Why did he have a throne?
What man has been cast out of heaven?
What man has walked in the midst of the stones of fire?
It is very clear that he was cast out before the recreation story.
Here you go
He was the angel in charge of worship.
The throne refers to God's throne, which he dwelt around. He wanted that throne because he wanted to be viewed as or more important than God.
Also, Ezekiel 28 is about as clear as mud as to whether he was talking about an earthly king, satan, or a combo of both (most theologians hold this theory).
