LDRs are designed so that their resistance depends on the intensity(brightness) of light falling on them. When in low intensity illumination (dark!), the resistance of an LDR is high. When in bright illumination, the resistance of an LDR is low.
Thermistors are designed so that their resistance depends on temperature. When subjected to low temperatures, the resistance of a thermistor is high. When subjected to a high temperature, the resistance of a thermistor is low.