No the first verse is not indicating that Allah will oppress but less than the size of the atom. At the time of revelation, Arabs considered the “dharra” to be the smallest thing or particle in existence. So the first verse is saying Allah won’t oppress anyone, even to this small extent.
As for the other verse, it’s saying nothing escapes the knowledge of Allah—even if something is smaller than a dharra He knows of it. So it’s just making it clear that He knows of the smallest things in existence.