Hi Andreas, from my understanding is, if Jan is using Topaz DN (AI) Auto applies both NR & additional sharpening based on what it sees. You can 'tailor' the amounts, but I guess folk just leave it to Auto and so you are allowing the software to take charge rather than the author being in charge!!!!
I would ask Jan to fwd the Raw, then you can see to a degree the camera set-up too, but what he has capture ie how sharp & the exposure, then, as we do in Wildlife advise with a better understanding and so Jan can improve both capture & how much he needs to address in his web set up.
That is down to f/stop & the compression the 500mm delivers David.