If you didn't shoot in RAW and only have JPEGs to look at, it's quite possible the grain setting was on. This might be reflected in the EXIF data of the JPEG. Not sure if C1 would show it but if you load it up in Fuji X RAW Studio, you should be able to see it under GRAIN EFFECT.
After 40 years with mostly Canon, both film and digital, a brief summer romance with Oly and a background with Nikon film, I cannot state how pleased I am with transitioning to Fuji and the X-T5. I thought I would never leave full frame but here I am and with a widening array of versatile primes at my reach I have no constraints and the files are very manageable. Muscle memory from EOS and dial/button placement was a thing in the beginning but now after a couple months it's been reset. Nothing but enjoyment and great images.