Why is PDLC considered to be smart?

The smartness of PDLCs is a result of its ability to change its transparency (technically called the transmittance) when an electrical stimulus is applied to it. This is normally by way of an alternating voltage, which exerts an alternating electric field across the PDLC material.
Nevertheless, the PDLC is only as smart as the control system which stimulates the change, which can be driven by a push button switch, a light sensor, or a building automation system.