I think the difference between fruit butters and jams etc. is the cooking method which doesn't involve pectin. The fruit is cooked into a thick paste but doesn't jell(y). The term butter is descriptive, it spreads, rather than etymolgical. After all creamed corn has no cream (so now they have to call it "cream-style corn" in Canada").
Incidentially in the Netherlands you find "pinderkaas" which translates as peanut cheese.