I had a horse die under my care. Owner- less than happy (to say the least). It caused ALOT of drama for me with things she had said (with absolutely no complaints previously in his care or treatment, and I check in regularly with anyone im working with to give them opportunity for complaints or any other thoughts) She DID have a vet out to investigate. The horse, though otherwise seemingly healthy, had a defect in its heart that wasn't outright noticeable. Nothing she, I or anyone else could have done about it. I don't have $25,000 dollar horses (short tall or otherwise) to offer her, but I did try my best to fix the situation. But, things got very nasty, very quickly on her part (and I can't say I was 100% polite when she started getting ugly, even though I DID sympathize with her). I also knew someone whose 6 month old filly snap it's own neck and still doesn't know how. I have had a horse die from mysterious reasons, though by no means quick. So, I can see where he's coming from.
As CA said, sometimes s*** happens. If she was incredibly concerned, she would have gotten the necropsy done. If she has the ability to send her horse to CA, I doubt she's lacking much in the finance department, even if he didn't offer to pay for it (which I don't see where he explicitly offered to).
Folks are not given enough information to judge the situation. (And, just as a side note, putting your horse on a diet is NOT enough to get them in shape, though, on the flip side, I would say almost 100% of the horses I've worked with were not in good physical shape to begin with, and it was part of my duty to not push their physical capabilities to the point of harming them)
I can see where people could use his training methods abusively. I don't see him as being abusive, and I doubt he'd put up with students who were. He is abrasive, yes. Rude? Most definitely. But, that doesn't make him evil or abusive I don't think.
Would I send my horse to the academy program? Most definitely not. Mostly because I'm a control freak. If I send a horse to a trainer, it would be where I could go to them at any point I desired, for whatever reason I desired (and I'm not so sure about that) regardless of how effective or how famous they are.
And, if I had ANY concerns whatsoever to begin with, I would have never sent them off. If I thought, for any reason, they were AT ALL responsible for the death of my horse, I would have investigated it further. If other people assumed it was mistreatment, I would have made sure to make people aware that it wasn't if I thought so.
It's just a lot of mudslinging with too many unknowns. Could have been anything (including but not limited to neglect or illness). Simply no way to tell.