Great, another bad groomer story.
It weighs heavy on my heart to hear about things like this happening.
In this case at least, it sounds like an accident, a split-second reflex in the heat of the moment and not a deliberate attempt to cause injury. Still no excuse, and I'm sure the groomer feels terrible.
Accidents like this can happen. It happened in my salon once--I didn't see what happened but apparently, my bather was bathing a cat, which was being very calm and docile in the tub. But when he turned the blow dryer on, the cat flipped out and attacked the bather, then went off the table and hit her head. Her eye immediately started to swell so we rushed her to the vet. I paid the bill, the cat did recover and was fine, but I felt absolutely horrible and so did my bather. He was in pretty bad shape as well, with severe bites and scratches. I had to send him to the doc-in-the-box for a shot of antibiotics.
I really don't think he threw the cat against the wall or anything like that, he didn't seem like that kind of person, but I guess I really don't know. He quit a few weeks after that incident anyway. This was probably 15 years ago and thankfully I haven't had anything like that happen since.