It looks to be operated from inside the house. The (wire?) being cut must be slim enough to easily slip through the tiny gap between the stationary and sliding doors’ frames. The wire in the house is secured there in some way, ready to be cute by the operator. I see nothing between the back of the basket and the blocks it’s resting on, so the secret of the contraption must be the wire which, via a couple of eye-screws on the back of the blocks, makes it way to the back of the basket and secured there, holding it in place. If that’s the way it works, a long section of wire goes on its merry way still attached to the basket; the quick forward movement of the blocks as the basket is loosed confirms that.