Why is this Diode and Capacitor present on the VBUS discharge path?
presumably as Vbus is charging up initially the diode switches ON and charges the capacitor almost instantly. Otherwise, the voltage is monitored through the 1K resistor. Any fluctuations in Vbus are filtered by the cap and the 470Ohm resistor. However, if there is a significant drop in the Vbus then a disconnect condition is presumed and the Vbus discharge path is activated on that pin. Here 1K was chosen, but if the 50mA would be preferred, then a lower resistor could also be used, like 100 Ohms, as long as the limit is respected for when the discharge path is activated.