From the datasheet OVP appears to have an upper and lower threshold, so OVP will kick in in case of open circuit, when the output voltage rises above the higher OVP threshold, but then the resistor network of the OVP itself will slowly cause the output voltage to drop below the OVP lower threshold, and the chip will turn back on, and the cycle repeats again and again. This effectively causes a voltage to be present at the output, albeit with high ripple and not well regulated.