Fairly unsurprising decision for France. It’s also an “accident du travail” if you are injured on your way to/from work, so surprising that they’d even attempt to dispute a business trip. Basically the only defense an employer would have is if there was negligence e.g. injured in a car accident on the way to work because you’re drunk or way over the speed limit.
Basically anything you wouldn’t be doing if you didn’t have to do it for work would be covered. Includes evening drinks if organised by the firm, so hardly surprising it extends to a business trip.