I stripped it last night, the bare frame weighs 4.65lb, the headtube is 1".
Assuming Kona measure from centre BB - centre top tube it is a 16", with the top tube and chainstay length being different between 1990 and 1991, it is the 1990 sizes.
Also on the rear brake boss, I found turquoise paint (primer?) and a small piece that is black with a red splatter on it.
I believe they measured size in 1990 from the outside of the bb shell to the top of the seat tube, which from what you say presumably means that this is a size 18 (or 18.75 from c-t). It would be interesting to know the c-c length of the top tube.
The weight seems to be roughly as expected for the size. Also the 1" head tube is a 1990 feature (and we can see it in Caramba Kid's photo of his).
I think there were quite a few who didn't like the 1990 fad for spatter paint, not even when Paul Brodie was the artist. I would imagine this must be the most likely explanation for the respray so early in its life.