This does look like it was printed on the kumquat. I don’t know whether it’s the case here, but this sort of thing sometimes happens when there is something printed on a bag or the plastic that food is wrapped in, and the ink can get transferred to the food.
I got the #1 kumquat in my bag (lemmy.ml)
A kumquat with the text “#1” stamped on it: found this way in the bag.