Mini-XLR is a connector, and can be used for anything. In your case it's used for ground/left/right and there is apparently no standard for the pinout, as seen here on reddit:
As one of the commenters points out, there _is_ a standard for XLR to TRS (Tip Ring Sleeve, aka 3.5mm or 1/4" connectors with two black stripes) in the case of balanced signals.
Balanced signals are mono not stereo, and "hot" and "cold" are the two terminals of a single audio channel. But in your case, you're dealing wtih a stereo signal that is NOT balanced.
Either way, it seems that pin 1 of your mini-XLR is going to be ground. You can test whether your headphones have pins 2 and 3 as left and right, using a multimeter on diode-check mode which will create a click in the appropriate ear when connected. If you bring the stuff tomorrow night we can do it together!
-jake