The driving force on a permeant ion–and hence the direction in which it flows when a conduction pathway for it opens–is determined *both* by its concentration gradient *and* by the voltage across the membrane (i.e., the electrical gradient). The membrane potential at which there is no net inward or outward flux for a permeant ion with a given internal and external concentration–i.e., where the chemical potential energy and and electical potential energy of the ion are equal and opposite–is the Nernst equilibrium potential.
Whether an ion flows in or out of the cell depends on the relationship between the Nernst equilibrium potential for that ion and the membrane potential. Unlike sodium and potassium–which must be regulated with very narrow concentration ranges both inside and outside the cell or else shitte goes to hell in a handbasket–cells have the ability to regulate internal chloride concentration within a pretty wide range. Thus, depending on the neuron and its physiological state, the chloride reversal potential can vary for an adult neuron between -40 and -70 mV.
If a neuron with a chloride reversal potential of -50mV is sitting at a membrane potential of -60mV when a chloride conductance is activated, chloride flows *out* of the cell and depolarizes the membrane. However, despite this channel opening event depolarizing the membrane, it can be inhibitory–i.e., it can make the cell less likely to fire an action potential.
Now see if you can figure out why this depolarizing conductance can be inhibitory!