Another "having thought of" ...
Perhaps FL140 has some relation. Typically somewhere above FL100 the fasten seatbelt is turned off and a bit later passengers are allowed to turn on approved electronic devises, give that a minute more and that could coincide with near FL140. Assuming a climb rate of 1-2,000 fpm.
Not a lot of attention is given to requirements for electronic devices to be turned off on these routes, I would postulate that this pax had even less of an inclination to adhere to these requirements if he was read into the objectives with the device...
One could further not disregard the probability that he had no control over the device at the one end of the scale, or that he had no disclosure from the courier/maker as to the intention of the device at the other end...