Two questions may be asked of the same event:
Who brings the event into existence? — the question of creation.
To whom is voluntary action and responsibility attributed? — the question of acquisition.
These are different questions. They should not be recast as requiring two independent creators of one event. Responsibility attaches to the human's particular relation to a voluntary act, not to an independent power of creation rivaling God.
The immediate purpose is to clarify the issue raised by Al-Balkhī and other Muʿtazilīs, not to exhaust every theory of kasb.