thm_w, which figure are you referring to?
If I assume Vin=75V, Vout=3.3V, Iout=0.A, L=33uH like in their reference circuit (Vin is actually given as a range, so I'm not sure, but I assume the inductance is given for the maximum input voltage) and plug this into their formula for the switching frequency ("Switching frequency can be estimated by below
equation") it gives me 637kHz.