A winter dawn is so thick with snow and fog that the speaker can barely see anything. Somewhere in it, a bird is flying, and it might be a crow, but the speaker can't be sure. All that reaches them is the sound of wingbeats, which slowly die away.
The poem's quiet trick is in its hedging words. "Maybe" crow, "would-be" distance: nothing here is quite settled. Even the distance isn't a real distance, because the fog won't let it become one. The title adds to the feeling by saying what the poem is not, as if even its form is uncertain. It has the three-line shape of a haiku, but the poet declines to claim it.
The speaker doesn't seem alarmed. The mood is hushed, a little lonely, and gently curious. It's the feeling of standing still in a blurred world and paying closer attention because you can't rely on your eyes.