If only two were used and it moved then it must be a brushed motor. Brushed motors only use two terminals for the operation of the motor, brushless use four terminals I believe (three windings plus ground?). The third could be for some sort of feedback or maybe special grounding.
Edit: One caveat - there are some BLDC (Brushless DC) motors that have integrated controllers - these have two power lines and many control lines. Other BLDC motors have integrated commutation sensors (hall effect sensors) - these will have three wires to drive the motor and five for the commutation sensors (three signal plus two power).
Thanks to the picture I can clearly see - that's a basic brushed DC motor. The third connection isn't really a connection - it might be a structural connection (to help keep the PCB attached to the motor) or just grounding to chassis. Does anyone else have a better idea what exactly the third solder blob is used for?