I'll try and remain objective and logical.
The fish are on unsuitable and potentially damaging surfaces, not long, soft grass or a wetted unhooking mat.
The way the photo has been taken does suggest the angler was on his own at the time. In turn this raises the question of how long the fish are out of the water for?
When I am fishing alone I find the length of time it takes to lift one fish from the water, take a self portrait and return it again is plenty long enough for my liking. Even then I have had, on occasion, to support fish in the water for some time before I'm happy they're good to go again.
How could you possible return seven (or maybe more) barbel safely even if there were two of you? Three people could only manage to support two fish each in the water.
I agree that sometimes we can be a little over-sensitive, after all we all hook and then pull fish from the water but, I can only see pointers to some questionable practices in this picture.
What if they were roach?
I would still be critical of the muddy / towel surface but smaller fish are easier to handle; their body mass is such that seven or more roach could easily be lifted out of the water in one net and in one go, photographed and returned in a similar time-frame to one bigger barbel.
Also silver fish seem much more tolerant of being out of the water than barbel anyhow, I've never had to nurse a roach or a dace in the flow before.