OK, here is my best guess.
Assume that Vref is connected to the inverting input of the comparator.
Initially the voltage at the pot slider is less than Vref, so Vout is low.
A small current will flow through the 300k resistor and diode (assume Vslider - Vout is greater than the turn on voltage of the diode), this load current will reduce the voltage at the slider by a small amount.
When Vslider exceeds Vref, Vout goes high (greater than Vslider), there is now no current in the 300k resistor and Vslider rises by a small amount so becoming sufficiently higher than Vref to prevent noise from "chattering" the output.
On a falling voltage at Vslider, when Vout goes low, Vslider is again loaded below Vref.
Thus there is hysterysis in this circuit.
JimB