I think it most likely this was trolling on the part of the Russians, part of a 'Grand Plan', if you will. Test NATO defences, lets Putin to indulge in a spot of faux outrage.
The jet(s) were warned numerous times to alter their vector, they didn't, they got what was coming to them (not the subsequent braying mob of pig-f****rs of course).
(The Belgrano comment ^ is most apt)