The resistor is technically not a pullup, as the circuit is analog, not digital. It is part of a voltage divider that provides a voltage level to the ADC input pin on the chip that ir proportional to the light level. Without the resistor, the LDR just pulls the input to ground.
The schematic makes this really confusing, as the resistor is in the power supply section, not by the LDR connector.
Agreed on all accounts. The schematics was indeed so confusing that I was in the middle of submitting an errata of the missing resistor when I finally located the resistor on the aforementioned power supply section.