Nancy Noll asked the Naked Scientists:I would be surprised if this is true. Most displays like this work by change of capacitance or the conductivity of the skin. Both of these depend on blood flow and sweat on the hand which are reduced by cold or sometimes circulatory illness. Placing another hand over will cause a change of capacitance.
... the team who put the display together said that they think the display works on magnetism....
Without knowing the exact type of sensor it is hard to be definitive.
It would be interesting to know whether the person has any circulatory problems, particularly those affecting peripheral circulation.