Whilst I am sure it is not the first time (may be it is), it is very unusual to hear of a service dog fouling mid flight, up to 3 times, according to the report.
Perhaps the dog was unwell and whilst I feel extremely sorry for the passengers who were sitting nearby, this is one of the consequences of dogs travelling in the cabin. In the US, small dogs (non service) can be carried in special safety bags, inside the cabin.
Part of my work involves flying dogs in private jets. We take precautions to cover these situations by having the correct cleaning materials and seat covers on board. Generally, we do not fly any animals, that are loose in the cabin, for longer than 4 hour legs. Aircraft needs to refuel and dogs defuel.