The difference is intelligence, which might be a better word than “intent.” A fence was built by someone with some measure of intelligence. An evolved feature is randomness combined with selection pressures, and sometimes it’s only there because it’s not sufficiently detrimental to be selected out.
Ok, intelligence is better than intent yes. But intelligence doesn't have a good definition and most people would say that it exists on a continuum. And when thinking of human-designed products, you can also say that there is selection pressure, and features can be selected out, etc. So I don't think there's a fundamental difference here.