Engines fingered
It's obvious that the problem was with some component of the engines. The really important bit is with which one?
If the fire started due to materiel or manufacturing defect in the original parts - that will be a big issue, which will make further use of the stockpiled motors difficult or impossible and put the continuation of the Antares program at risk.
If that was a fault in the new components (Aeroject has designed new articulated feed lines to increase the gimbaling angle) - that will be a much lesser issue. One that can be easily fixed in the future.
Let's just wait and see what the investigation will show.