Nivellen and Geralt don't know each other in the short story, Ciri isn't there aswell because originally the story took place many years before Geralt had anything to do with Ciri, we learn from almost the start the reason why Nivellen was cursed (and in the short story he is more bear-like and not wild boar-like in the show), so the reader - aswell Geralt - shouldn't like Nivellen's character but as the story goes on, it is more and more obvious that Nivellen has changed and matured through the years and really regrets his actions when he was young and now treats everyone well and fair.. so the original short story is about redemption, even though the reader (and Geralt) at the start either hate or don't like Nivellen, at the end atleast they saw that he was really changed compared to what he was like in the past - redemption..and in the show his character evolution is "ha, he is a good friend of Geralt, that means he is probably ok", then "well, he did some bad things but they aren't that bad in all honesty" to "what? he raped a priestess? well fuck him alright" .. it went from the original short story's " too quick to judge" to shows "humans are the real monsters" (which is almost repeated in every scene in the show)
What I don't like is that each book short story had a different meaning, moral lesson and theme but the show almost always goes with the only one, again the "humans are the real monsters".. even the elves are in the show victims, even though in the books they landed on the Continent only after dwarves and gnomes who already lived there for houndreds of years and the first thing the elves did was starting many wars against mostly the dwarves (and some other original races on the Continent, which don't exist in the Geralt timeline) and the main reason why elves lost so much power against the humans was the fact that only young elves are fertile and humans started to win against them in numbers because they can more freely reproduce.. only after many years after the humans came to the Continent, they started some wars with the elves