The author of that quote, David Chapman, is a very interesting man! An expert on artificial intelligence, a philosopher, and novelist, as well as a long time Buddhist. But the idea that we can never have complete knowledge is not specific to Buddhism. It is built into mathematics for example, as set out in Gödel's Incompleteness Theorems. Then we have the Heisenberg Uncertainty Principle which limits our knowledge of the quantum states of sub-atomic particles.
I think what David is trying to get at here is that the answers to our big questions cannot be had on the same level as the question. Unawakened beings do not see experience clearly enough to ask good questions. So for example we might be asking "What will make me happy?" And we'll expect the answer to be something simple, and probably related to pleasurable sense experience (this belief is deeply ingrained even in people who profess to believe it is not true). But search as we may we cannot find the one thing that will make us happy. Some forms of Buddhism tell us that happiness is not attained through acquisition, but through relinquishing. The question "What will make me happy?" can never have a satisfactory answer because it's framed in a worldview that precludes ultimate happiness.
The idea of "groundlessness" is a strong feature of Tibetan Buddhist teaching. Another author who talks like this is Pema Chödrön. My take on this might be different to David's and Pema's. All that we know about anything comes through experience. When we say "things arise in dependence on conditions" we mean experiences arise in dependence on conditions. And experiences themselves, are neither existent, nor non-existent. When we have an experience nothing "new" comes into being and when an experience ceases, nothing existing ceases to exist. Experiences are empty of self or anything related to self, they are empty of self-existence (i.e. an existence for which the thing itself is a condition). Therefore in experience there is nothing which is stable or lasting. When we say "things are impermanent" we mean experience is impermanent. And because experience is impermanent it cannot offer permanent solutions - not to unhappiness or suffering or any of our other problems. Experience simply cannot be relied on.
Some Buddhists do claim to "perfectly describe the nature of this world". But a close reading of early Buddhist texts and, for example, the Perfection of Wisdom texts, makes it clear that they are not concerned with the nature of the world oe reality, but with the nature of experience. The idea that Buddhism describes the nature of the world is an error that crept into Buddhism very early on, and there have been repeated reformations to re-establish the focus on experience.