The word 'return'
Yes, 'return' is an accurate translation. The Hebrew verb is shūb (שוב), and means 'to turn back'.
But what is 'spirit' referring to?
Ecclesiastes 12.7 uses a handful of certain words and ideas: the body is made of dust and returns to the earth upon death; the spirit is from God and returns to him upon death. We're in the same realm of thought as Genesis 2-3, so we should turn there for further consideration.
Genesis 3.19 says that when Adam dies, his body will 'return' to the 'dust', referring to decomposition. Turning back a chapter, to Genesis 2.7, we see God create the man's body from the 'dust', and then God
breathed into his nostrils the breath of life, and the man became a living soul.
The Hebrew word for 'breath' here is neshamah (נשמת), and is synonymous with the word ruach (רוח), the word translated as 'spirit' in Ecclesiastes 12.7. Both words may be translated as either 'breath' or 'spirit', and they are occasionally used together to describe this breath/spirit. For example:
- the neshamah of the ruach of life (Genesis 7.22)
- at the neshamah of the ruach of his nostrils (2 Samuel 22.16 / Psalm 18.15)
- By the neshamah of God they perish, and by the ruach of his nostrils they are consumed (Job 4.9)
Because the meaning of these words is so consistent throughout the Hebrew scriptures, we can rightly read Ecclesiastes 12.7 in relation to Genesis 2-3. The person is not the same thing as their neshamah // ruach. Rather, the person is made alive by their neshamah // ruach, which is given to them by God, and returns to him when they die.1
Within the biblical authors' general understanding of what 'makes' a human, they did not appear to consider the human spirit as personal in and of itself. Consequently, the claim that humans used to be angels, and become them again after dying, is entirely speculative in relation to Ecclesiastes 12.7.
1 One long-standing opinion among Jewish theologians is that life begins when a newborn's head has exited the womb, and has taken its first breath (neshamah // ruach), an event called 'ensoulment'. This opinion is largely based on the description in Genesis 2.7 that Adam became a 'living soul' when God breathed his neshamah into him. Thus, death is a reversal of the process: the person dies, and their breath/spirit returns to God.