Being in control does not mean achieving what you “want” or intend.
You are in control of your car, even if you unintentionally hit a tree. Likewise, Pollock controls his paintbrush, it is held by his hand which only he can move. If he flicks paint on his friend’s new jacket that might not be his intent, yet he is still 100% responsible for that outcome.
To the extent that you do not control a physical paintbrush, you lose your claim to copyright.
If you left a wet brush on a piece of paper and came back the next day to find the wind had blown it across the paper leaving a paint streak, that paint streak could not be copyrighted. You fully relinquished control of the brush to the wind.
Arguably the same is true of the wind. So to claim copyright, you cannot relinquish control to an inanimate object. Not to the wind, not to an AI.