This is called extortion inoculation. BS enough times and nobody will pay BTC to any extortionist.
They payment method that a terrorist is really not relevant. Most governments refuse to negotiate with terrorists because of the risk that other groups will simply do similar things in order to extort money from governments.
The reason why they are asking for payment in bitcoin is because it is very easy to 'move' bitcoin and it is difficult to trace the identity of someone who owns/controls a specific address.
EDIT: they are really just highlighting features of bitcoin