More specific Quaternion.LookRotation

Quaternion.LookRotation actually has two parameters. The first parameter is the major-axis, the z-axis. The second parameter is a hint direction vector which defines the desired up direction. If you don't pass a direction vector for the up direction it default so Vector3.up. So the rotation will always be oriented in a way so the y axis is closest to the world y axis.

If you just want to randomly rotate the object around the z axis you can use Quaternion.AngleAxis to create a random rotation around the z axis and multiply the result of Quaternion.LookRotation with that one. Rotating around a different axis than the z-axis wouldn't make much sense since it would change the result of LookRotation so it won't face that direction anymore.

 Quaternion.AngleAxis(Random.Range(0f,360f),hit.normal) * Quaternion.LookRotation(hit.normal);