Thanks Charles, that could have been. A brighter light may or may not blow the fuse, I don't know. Obviously, mine didn't blow the fuse.
Why Kawasaki made that small housing so seemingly air tight, I don't know either; it's not as if I am submerging the bike in water up to that light height.
I don't know either if it was the bulb that got brighter causing the housing to melt, or the heat building up inside that overheated the light. How long it has been melting, I don't know either.
Now that I drilled holes in the bottom I can't check if after a long ride if the housing felt very warm or not. Also, I don't know if rain water affected it by blowing in any very small crack.