Is my understanding of this level shifter correct?
Yes, if you are planning to translate logic signals from 3.3V to 5V domain. This level shifter should do the job. EN signals controls the internal switch, so if you pull it high to ref B the translation will take place, so
if A1 is high(3.3V) or low(0V), B1 will be correspondingly high(5V) or low(0V)
same goes for A2 and B2.

If EN is low, all I/O pins will be high impedance. 

The translation works in both direction but make sure Vref_b > Vref_a +0.8 V. So you can't put 5 V on Vref_a and 3.3 V on vref_b.