These token cards are no more nefarious than the cheapo "wallet sized" LCD calculators given out by realtors. Same basic device.
A lot of folks strap these things to the handle of the computer briefcase, just like you would a luggage tag. It's convenient that way.
So its easy to imagine a token coming loose from the bag and dropping on the floor ... under the seat, where the briefcase is stored.
I see no mystery here, aside from the complete overreaction of the stewardess.