In the August 2017 article by Michael Ash, After the Manner of Their Language: The Key to Wisdom, he writes:

Many Latter-day Saints have found support for a global flood within the pages of the Nephite record, but a closer examination reveals that such a conclusion is not required. In Ether, for example, we read that “after the waters had receded from off the face of this land it became a choice land above all other lands” (Ether 13:2). We know that the Jaredites (as interpreted by Moroni) were familiar with Noah’s ark (Ether 6:7) so these verses imply a world-wide global flood. It’s important to remember, however, that the Book of Mormon peoples themselves didn’t experience the flood. Neither Moroni nor Ether would have known from personal experience that the waters receded from the face of the New World. They believed that this is what happened, but that’s not the same as claiming to be witnesses to the event.

It’s entirely possible that either Ether, Moroni, or even Joseph Smith included the comment about the waters receding from the land based on their understanding of the ancient New World and according to their interpretation of the Noachian flood as recorded in Genesis.