Sure it is. "... and for that reason the holy Child shall be called the Son of God." Which means that he wasn't called that before, which again agrees with John 1:1, where He is called "The Word" and 1 John 1:2, where He is called "The eternal life".
You said "You don’t call someone something that they are not."
That is not true, we do that all the time. How old was President Trump when he entered the military school?
Obviously he wasn't the president back then. But we still refer to him as the president, because that is what we know him to be today, even though back then, he was decades from becoming the President.
Likewise, Jesus can say that He, the Son of God, was with the Father, sharing His glory before the world was, even though He didn't become the only begotten Son of God until He was conceived in, and born from Mary's womb. John 17:5 What Jesus appears to be saying is that He is the same Spirit now as He was back then.
The same could be said of Jesus when He said, "Your father Abraham rejoiced to see My day, and he saw it and was glad." (John 8:56) and "before Abraham was born, I AM." John 8:58 Was Jesus called "Jesus" back then? No. Likewise, it appears that He was not called The Son of God back then. We know that He was the Word in verse 58 and could have been called Melchizedek during the time of verse 56.
I think we really do have an issue here of some people who do not understand how the English language can be used and understood.