Alchemists formed the basis for modern day Chemistry. They were wrong and had no idea why they were able to do the things they did but that doesn't mean they weren't able to find truth.
Vikings commonly threw bones of their ancestors in smelting furnaces because they believed the souls would strength the iron. They were right, bone and poor quality iron formed a rudimentary type of steel which did indeed make a stronger blade. The explanation is entirely chemical, but they were able to reach a truth beyond their current level of scientific understanding.
Acting like people from the past were just big dummies who did things for no reason is idealism. They couldn't scientifically understand why these things occurred but they still understood the effects of the world around them.
The truth in this example is that you can make iron stronger by adding bones. Being incorrect about the process doesn't make the result any less truthful.
In that case, it's elephants all the way down. I can understand how trees work and discover new things about them without understanding how sub-atomic particles interact in their leaves. You think having no understanding of the underlining phenomenon makes the things you observe and discover above it untruthful. But everything we know about the universe today relies on principles we don't understand yet. By your own definition, all of modern science is false because we haven't yet filled in certain gaps.
Was the Plum Pudding model just something J.J. Thomson made up? In a historical epoch in which ghosts, werewolves, and gods were presumed to exist, this was an extremely logical explanation. Being wrong doesn't mean these people were just guessing and talking out their ass.