The two descriptions do not contradict each other. MAX1481 has a failsafe feature where there is a weak pullup to VCC at input A and a weak pulldown at input B. When input is open, input A is pulled up and input B is pulled down, pulling differential voltage across A and B to be above 200mV, and ensures that RO outputs a logic-high. However, since the internal pullup and pulldown are both very weak, any external connection will override the internal pullup and pulldown. It only maintains a logic-high under open circuit condition, and does not conflict with the input threshold.