For all we know, and likely, the horse was being treated with an anti-inflammatory the same way people take Motrin. These riders have back-up horses that can be used if there is a serious problem. And while I haven't read the details - I won't make judgements as to when the drug was given, WRT the test - it may have been as a precaution after the flight and settling in.
Don't jump to the extreme. These are incredibly valuable horses, and tend to be very carefully tended - it's not the racing game with millions and millions of dollars at stake. The flying conditions for these level of horses are amazing - not freezing in the hold of a standard plane. There are specialty containers - essentially box stalls - for the horses, with all kinds of padding, and grooms travel with them. They're probably more comfortable than people flying coach.
It's unlikely that anyone at this level would force their horse to perform in extreme pain. Even with a drug - that would affect other things in the animal's performance.
Surely at times. But, I wouldn't jump to paint the entire USET as evil tyrants forcing their animals to be tortured. Certainly there are cruel or less caring individuals in any sport - but, especially dressage horses - it's a big intelligence and training teamwork thing. And incredibly difficult to get to Grand Prix level - it requires amazing trust, bond, love, respect, understanding on the part of the horse and the rider. Horses don't learn those moves out of fear, and certainly can't perform in pain. So, who knows the details - but, again. IME I would tend to give some benefit of the doubt. Remember - people have been disqualified over taking cold medicine which they didn't realize was on the forbidden list.
Ellice