The harbor was closed as far as I know. Ships flying the American flag were fired upon. A confrontation with the Fox's ships first would have been politically better for the Confederates. As you know the history books in schools never mention why Beauregard had to fire on the fort, never mention the two fleets sent by Lincoln, just like the Northern press did after the action. Would have been a lot different if the firing started with Fox's attempt at reenforcement.

The first recorded shot by the Union was Fox firing on an unarmed passenger ship waited outside the entrance to the harbor for permission to come in. Fox did not know what ship it was.

David