I suppose he means that a small microphone/speaker setup near an ATM machine's keypad could allow you to track the position of the finger and get the corresponding keypresses without any intrusive modification to the ATM itself.
Of course that would only be valid if you proceed to then steal the person's card right afterward, so all in all, not that useful.
Isn't it easier to just put up a small camera? Then you can also record the card's number if you fail to steal it afterwards.
It would be easy to build a device that did something similar to this and captured pin codes on ATM machines.
Currently you can see everywhere ATMs are asking you to visually check that keypad and card-input looks exactly like on picture. With this technology, you don't need to make a fake keypad to "hear" PIN sequence, you could just "listen" to it from somewhere else, some place not seen well.
I guess he means that you can place a smartphone near an ATM and catch the PIN-code with this technology somehow.