Jabr (compulsion) becomes an error when a human being is regarded as entirely compelled in their actions, as though human choice and acquisition had no standing at all.
This view treats the servant's act in a way that leaves no meaningful voluntary attribution to the servant. The balanced position avoids that extreme.
Affirming Allah's power and His creation of acts does not require holding that the human being is altogether devoid of choice. Treating a person as utterly compelled is the error of jabr.