When Jesus was on the cross, he cried out to God. Does this prove then, that he never claimed to be God? Otherwise, why would he say these words? Let’s look at the Scripture:
scorned by mankind and despised by the people.
7 All who see me mock me;
they make mouths at me; they wag their heads;
8 “He trusts in the Lord; let him deliver him;
let him rescue him, for he delights in him!”
14 I am poured out like water,
and all my bones are out of joint;
my heart is like wax;
it is melted within my breast;
15 my strength is dried up like a potsherd,
and my tongue sticks to my jaws;
you lay me in the dust of death.
16 For dogs encompass me;
a company of evildoers encircles me;
they have pierced my hands and feet—
17 I can count all my bones—
they stare and gloat over me;
18 they divide my garments among them,
and for my clothing they cast lots.
The Jewish people considered this a prophecy of the Messiah to come. Jesus was literally fulfilling this prophecy as he was hanging on the cross.
It is why he was quoting this. He was declaring that He was the One, and here was the proof – fulfilled prophecy.
While it does not say specifically that this was the Son of God, we have hundreds of prophecies that describe the Messiah to come. The most telling is one of Jesus’ favorite during his ministry in Daniel 7:13-14:
and behold, with the clouds of heaven
there came one like a son of man,
and he came to the Ancient of Days
and was presented before him.
And to him was given dominion
and glory and a kingdom,
that all peoples, nations, and languages
should serve him;
his dominion is an everlasting dominion,
which shall not pass away,
and his kingdom one
that shall not be destroyed.
Jesus is indeed proclaiming he is deity. That he was the one who fulfilled Scriptures. The cross in particular was a fulfillment of the David prophecies.

