That headline is not true. Because we don't actually have potatoes growing on Mars, there is a lot of information we could potentially be missing, like microbe

That headline is not true. Because we don't actually have potatoes growing on Mars, there is a lot of information we could potentially be missing, like microbes we haven't discovered, effects of the radiation and little atmosphere, or (going for an extreme example here) a rabbit-like creature that we have never been able to detect yet, that eats the potatoes while we're not watching. What we've accomplished with this experiment is only to "Grow potatoes in the closest approximation to Mars setting that some scientists thought of".