It means exactly what it says, pertaining to the creatures of the sea and sky, created on day 5. But on day 6, the text says God created the creatures of the land, which were produced by the earth. I am not reading anything into the text. I'm stating what the text says. Where does the text say, the creatures were created from dust, as was man?
Actually, the whole of creation on days 1 through 6, with the vital exception of man, was just letting nature take it's course, so to speak; a permissive creation. In every case, God says, "Let there be . . ." not, "Light, be," or "Sky, be," but, "Let there be light. . . " But in the case of man, he deliberates, Father, Son and Holy Spirit, "Let us make man in our image." And then he made man from the dust.
So, verses one and two suggest (in light of day 6) that while the earth was still formless and empty, life was "coming to the surface," before time began, the earth giving birth on day 6 of time, especially since at that time, "the Spirit of God was hovering (the Hebrew suggests explosive energy) over the surface of the waters." On day 6, God says, in essence, Let the earth give birth to land creatures--permissive. Then God says while it is still day 6, "Let us make man in our image,"--proactive--from the dust of the ground.
I imagine a fully developed and grown zebra struggling his way from beneath the very surface of the earth, jumping up on all fours. Yet I believe the earth is fewer than 6000 years old.