In practice, you often end up with multiple nested control loops on this kind of system, each of which is closed.
You might have a voltage controller deciding how much to turn on the motor transistors based on voltage feedback...
You might have a motor speed controller which decides what voltage to give the motor based on speed feedback...
With another position controller deciding what speed the motor should try to go based on position feedback...
And then the magical-mirror-aiming thing deciding where the position controller should try to point it based on other feedback.
And then the industrial process controller deciding how many mirrors should be pointing at the thing based on temperature feedback...
And some other controller deciding what the temperature should be based on process feedback...
And then humans turning the knobs on that controller based on QA feedback.
(And each of these control loops usually gets at least 2x slower as the one it encloses).
Open/closed loop basically means whether you check the result of an actuation. What we're really talking about is the point at which the loop is closed.
A completely open loop would run the motor for the predicted time.
A simple closed loop would run the motor until the mirror is pointing at the predicted angle, using an encoder to know where the mirror is pointing. The control loop encompasses a mechanical part of the system, but not the end-thing we want controlled. Or put another way, the loop is closed for actuator angle but is not closed for where reflected light goes.
A better closed loop would run the motor until the mirror is reflecting sunlight exactly where we want it-- using magic to know where the light from this mirror is going.