Rr95

My 2001 Audi A4 2.8L auto seems to read just a tiny bit over the 90° C mark when warmed up ..never goes higher than this unless the car is shut off when hot and restarted after 5-10 minutes then the coolant temp would be near or at the first small line after 90c and will quickly (within 10-20 seconds) drop back down to the resting position just over 90°c. I know my 97 A4 with 2.8 has a gauge that reads 90° c all day everyday but since all cooling functions seems to be working and car runs like a champ I was wondering if maybe the previous owner just had a aftermarket thermostat put in or something. Let me know your thoughts please!
https://imgur.com/a/VKimMpy
Picture of the normal temperature after 30 or so minutes of city driving, I've driven it up to around an hour the temp gauge never really moves from that point. Could this be a temp sensor issue? Let me know thanks!