I had a similar event with my two bull terriers (dog & bitch) but it happened whilst they were crated up together bombing down motorway
never had any bother with them prior to this feed, play and bed together. been all over the country with em in a large transit cage plenty of room. Must just have decided to have it out there and then. No growling or nowt just instantly full on battle
by the time I had managed to get over on to hard shoulder and run to back of vehicle, cage was bumping all over inside of car missus and kids screaming dogs rolling round like mad blood and snot everyw