Maximum Voltage at CBOOT resistor and capacitor
16V in 3V3 out gives D=0.2
F=2.1MHz so Ton=95ns Toff=381ns
e=L di/dt so di=e*dt/L
With L=12µH, e=Vout, dt=Toff: di=100mA
So the 12µA value is correct for an output current of 450mA if you want 20% ripple current. You could use 10µH.
I guess the difference in inductance values comes from the fact the 2.2µH inductor was calculated for a much higher current of 2.5A. Designing for a target value of current ripple like 30%, with a higher current, a higher current ripple is allowed, which gives a lower inductor value. Notice in the datasheet they also increase the output cap, to compensate for the extra current (and therefore voltage) ripple.
But at 400mA, with a 2.2µH inductor, it would work in discontinuous mode. 12µH means it will work in continuous mode, which gives less output voltage ripple.