I'm not sure (without further research) exactly what's going on in these video's, but anyone who creates one of these devices, the most stupid thing you could do would be to put a demo video on youtube of how to do it.
However there is a possibility I haven't seen posted yet.
The contents of a CPU whether in a PC, fruit machine, atm, calculator, digital watch etc can be read at a distance of several meters because of the electromagnetic signals (radiation) given off, if you have the right equipment.
I first heard of experiments being done in the early 90's by Department of Defence, for fairly obvious reasons. It was later proven that again, with the right equipment, you could change the contents of the cpu using similar methods.
Fast forward to 2014, I would imagine the equipment to do so would be much cheaper and smaller now. It was only a matter of time before someone used it for nefarious purposes.
I'm not sure of the tech required, a cursory google search turned up nothing, but if anyone's really interested I'll keep looking.
Theoretically, with the right equipment, you could empty the hopper of every machine in a seaside arcade while sitting on the beach.
I do remember one thing though, that the equipment to do this would be hyper sensitive to electro magnetic flux signatures.