Q) How is the hysteresis set on this design.

A) The internally to the IC there is no hysteresis so external hysteresis is added by placing a 4.7pF capacitor between the MOD pin and the SNS pin.  this creates a capacitor divider that gives a few milivolts of offset so the switcher will stay in its new state instead of bouncing back to the old state right away.  If a high side sense is used and the SNS signal is positive with respect to ground the capacitor should be placed between SNS and the collector of the transistor connected to the MOD pin.  This inverts the signal to the correct polarity.