I'm not sure of the accuracy of such statement.
See the birth narratives in Matthew 1 and Luke 1.
Some think that the New Testament teaches that God begot his Son before the universe was created.
Now we have the issue of preexistence. As I mentioned to you earlier, all trinitarians, binitarians and the majority of unitarians believe in literal preexistence.
I’m a Jewish monotheist. I believe in notional preexistence, not literal preexistence.
Some have thought that God begot his Son at the time of his baptism, or his resurrection. This is known as adoptionism.
Some think like you have said.
Everyone is right? No.
It doesn’t matter who is right?
The meaning of "begetting" a son remains a mystery.
Not at all.
The text says:
The Holy Spirit will come upon you, and the power of the Highest will overshadow you; therefore, also, that Holy One who is to be born will be called the Son of God.
That should remind you of what happened in the Genesis account of the creation of the heavens and the earth.
Yahweh was at it again.
So, according to the angel, Jesus was going to be called the Son of God because of a special action of God's power on Mary. What was the exact nature of such action? We don't know.
A human person was miraculously created by Yahweh in the womb of a virgin (Mary).
To “beget” a person is to bring a person into existence / being. We see this clearly expressed in passages of scripture where we read “X beget X”.