Adding Hysteresis to Supply Voltage Supervisor
Take a look at Figure 1 in the link you gave. It explains that the reset output has a pull-up Rp to voltage V2 and reset output is fed back to VS+ via resistor Rh. The reset output is clearly open-drain output so either reset is pulled to 0V by the chip, or it floats to V2 via Rp. That is why VS+ is pulled down to 0V only via Rh, and pulled up to V2 via Rh and Rp.