I know some people are better at mentally visualizing things than others, so I drew up this *very* rudimentary diagram.
(I apologize, as MSPaint + flaky mouse = jiggly lines)
Under *normal* track-switching procedures as described by board57796, a train being switched from the Epcot beam to Express would leave the TTC and follow the beam marked in solid pink. When they reached the far right-hand side, they would stop, wait for the switch to move, and then drive backward along the dotted pink beam to the Express beam. Following the end-of-night procedures, they'd continue on through the station and continue heading toward the Polynesian in "reverse".
But, according to board57796's hypothesis/description, what apparently happened is that Pink followed the solid pink beam, stopped, and then backed up along the same solid pink beam. I've marked Monorail Purple's location in blue. Once Pink passed through the station, it collided with Purple approximately where the blue line ends on the beam, in the area between the ticket booths and the station.
-Rob