The expression Son of God was used in old
Israel for very pious persons. Solomon for example was a Son of God too:
1 Chron 22:9‑ 10
Behold, a son shall be born to thee (David),
who shall be a man of rest, and 1 will give him rest from all his enemies round
about: for his name shall be Solomon, and
he shall be my son, and 1 will be his father.
You recognise, that this expression cannot be
meant literally. Jesus himself says, that we all are the children of God:
Mt 5:9 Blessed are the peacemakers: for they
shall be called the children of God.
Mt 5:16
Let your light so shine before men, that they
may see your good works, and glorify your Father which is in heaven.