Figure 1. The module 5 V to 3.3 V regulator. Source: XBee Regulated - V14.
The 500 mA specification is the maximum the board can supply at 3.3 V, not what the board itself consumes. This is determined by the MIC5219 voltage regulator.
Actual consumption of the board will be the tiny current required by the level shifters (if I understand its function correctly) and whatever the board is feeding at 3.3 V.