The pax were actually deaf-mute and were not accompanied by any ABPs. It would be very presumptuous to ask ABPs to take complete responsibility for them. The decision not to carry them was based on the fact that in an emergency they would be unable to communicate with cabin crew or even other pax.
I suppose that if an emergency had occurred and any of them has been injured there would be various lawsuits flying around - it would be grossly unfair if an ABP who voluntarily helped out became the subject of such a lawsuit.
I expect Ops manuals will be updated to include this particular disability - until the next case.......