The angel did not claim that. Christians claim that the verses mean what they do not mean.
Acts 1:9-11 And when he had spoken these things, while they beheld, he was taken up; and a cloud received him out of their sight. And while they looked stedfastly toward heaven as he went up, behold, two men stood by them in white apparel; Which also said, Ye men of Galilee, why stand ye gazing up into heaven? this same Jesus, which is taken up from you into heaven, shall so come in like manner as ye have seen him go into heaven.
The disciples were staring up into the sky as the spirit of Jesus was taken up to heaven out of their sight. The two men dressed in white (angels) came along and asked why they were staring up into the sky because they wondered why the disciples were staring up into the sky. Then the angels told the disciples that the same spirit of Jesus that was taken up to heaven will return just as it went to heaven.
The verses do not say that the disciples saw a body go up. It was the Christ Spirit that ascended, not a body, which is why the angels wondered why the disciples were staring into the sky, since there was nothing to look at. That makes perfect sense since angels can see spirits.
Descending from heaven upon the clouds means that the spirit of Jesus, the Christ Spirit, will be made manifest from the heaven of the will of God and will appear in the form of the human temple. Though delivered from the womb of Mary, Jesus in reality descended from the heaven of the will of God. Baha’u’llah descended
in like manner, from the heaven of the will of God.
“But as the clergy have neither understood the meaning of the Gospels nor comprehended the symbols, therefore, it has been said that religion is in contradiction to science, and science in opposition to religion, as, for example, this subject of the ascension of Christ with an elemental body to the visible heaven is contrary to the science of mathematics. But when the truth of this subject becomes clear, and the symbol is explained, science in no way contradicts it; but, on the contrary, science and the intelligence affirm it.”
Some Answered Questions, pp. 104-105
Jesus never claimed that He was going to return to earth. Christians claimed that.
John 17:4 I have glorified thee on the earth: I have finished the work which thou gavest me to do.
John 17:11 And now I am no more in the world, but these are in the world, and I come to thee. Holy Father, keep through thine own name those whom thou hast given me, that they may be one, as we are.