The ADG324x family are level translators that is capable of translating voltage levels from high to low only. This statement can be supported by the Truth Tables and is further discussed at the Mixed Voltage Operation, Level Translation Section of the respective datasheet. The bidirectional term meant in the datasheet is that Ax and Bx pins can be either an input or an output. This means that the part is smart enough to detect what pins (either Ax or Bx) are used as the input pin and automatically makes the other side as the output pin. Let us put it this way, if Ax is used as an input pin (with higher voltage level), then the part would automatically make Bx to be the output pin (with translated lower voltage level). This is also the same if Bx pin is used as the input pin then Ax pin will be the output pin.
In summary, the ADG324x family are bidirectional level translators because there is no impedance to signal direction, but it cannot translate the voltage up.