Yeah, 52-59 degrees C is fairly standard operating procedure for high-end NVIDIA cards.
However, to answer your question directly, your culprit is likely that your card is sensing that it’s running lighter, so it’s also dropping your fanspeed to save power and reduce noise (there’s usually a target temp for each profile). If you undervolt in combination with locking fanspeed (remember to turn it back to auto when playing a game!) you should see your temps drop to 51 degrees or so.
