John thought he was a angel and was told otherwise.
He was an angel. It was actually one of the 7 vial angels:
Rev 21:9
And there came unto me one of the seven angels which had the seven vials full of the seven last plagues, and talked with me, saying, Come hither, I will shew thee the bride, the Lamb's wife.
Rev 21:10 And he carried me away in the spirit to a great and high mountain, and shewed me that great city, the holy Jerusalem, descending out of heaven from God,
Rev 21:11 Having the glory of God: and her light was like unto a stone most precious, even like a jasper stone, clear as crystal;
Rev 21:12 And had a wall great and high, and had twelve gates, and at the gates twelve angels, and names written thereon, which are the names of the twelve tribes of the children of Israel:
Rev 21:13 On the east three gates; on the north three gates; on the south three gates; and on the west three gates.
Rev 21:14 And the wall of the city had twelve foundations, and in them the names of the twelve apostles of the Lamb.
Rev 21:15 And he that talked with me had a golden reed to measure the city, and the gates thereof, and the wall thereof.
Rev 21:16 And the city lieth foursquare, and the length is as large as the breadth: and he measured the city with the reed, twelve thousand furlongs. The length and the breadth and the height of it are equal.
Rev 21:17 And he measured the wall thereof, an hundred and forty and four cubits, according to the measure of a man, that is, of the angel.
Rev 21:18 And the building of the wall of it was of jasper: and the city was pure gold, like unto clear glass.
Rev 21:19 And the foundations of the wall of the city were garnished with all manner of precious stones. The first foundation was jasper; the second, sapphire; the third, a chalcedony; the fourth, an emerald;
Rev 21:20 The fifth, sardonyx; the sixth, sardius; the seventh, chrysolite; the eighth, beryl; the ninth, a topaz; the tenth, a chrysoprasus; the eleventh, a jacinth; the twelfth, an amethyst.
Rev 21:21 And the twelve gates were twelve pearls; every several gate was of one pearl: and the street of the city was pure gold, as it were transparent glass.
Rev 21:22 And I saw no temple therein: for the Lord God Almighty and the Lamb are the temple of it.
Rev 21:23 And the city had no need of the sun, neither of the moon, to shine in it: for the glory of God did lighten it, and the Lamb is the light thereof.
Rev 21:24 And the nations of them which are saved shall walk in the light of it: and the kings of the earth do bring their glory and honour into it.
Rev 21:25 And the gates of it shall not be shut at all by day: for there shall be no night there.
Rev 21:26 And they shall bring the glory and honour of the nations into it.
Rev 21:27 And there shall in no wise enter into it any thing that defileth, neither whatsoever worketh abomination, or maketh a lie: but they which are written in the Lamb's book of life.
Rev 22:1
And he shewed me a pure river of water of life, clear as crystal, proceeding out of the throne of God and of the Lamb.
Rev 22:2 In the midst of the street of it, and on either side of the river, was there the tree of life, which bare twelve manner of fruits, and yielded her fruit every month: and the leaves of the tree were for the healing of the nations.
Rev 22:3 And there shall be no more curse: but the throne of God and of the Lamb shall be in it; and his servants shall serve him:
Rev 22:4 And they shall see his face; and his name shall be in their foreheads.
Rev 22:5 And there shall be no night there; and they need no candle, neither light of the sun; for the Lord God giveth them light: and they shall reign for ever and ever.
Rev 22:6
And he said unto me, These sayings are faithful and true: and the Lord God of the holy prophets
sent his angel to shew unto his servants the things which must shortly be done.
Rev 22:7 Behold, I come quickly: blessed is he that keepeth the sayings of the prophecy of this book.
Rev 22:8 And I John saw these things, and heard them. And when I had heard and seen, I fell down to worship before the feet of
the angel which shewed me these things.
Rev 22:9
Then saith he unto me, See thou do it not: for I am thy fellowservant,
and of thy brethren the prophets, and of them which keep the sayings of this book: worship God.
So the angel called himself an angel that was sent to show these things, and so when John calls him an angel, he is correct.
Let's go back to the 7 vial angels:
Rev 15:6 And
the seven angels came out of the temple, having the seven plagues,
clothed in pure and white linen, and having their breasts girded with golden girdles.
Rev 15:7 And one of the four beasts gave unto
the seven angels seven golden vials full of the wrath of God, who liveth for ever and ever.
Rev 15:8 And the temple was filled with smoke from the glory of God, and from his power; and no man was able to enter into the temple, till the seven plagues of
the seven angels were fulfilled.
