Even if they didn’t evacuate, they should have moved some of these people out of low-lying areas and blocking off flooded roads.
You don’t evacuate everywhere. You evacuate the areas you know that have a strong chance of flooding. He’s creating a straw man argument (”you can’t evacuate everyone”) to hide the incompetence (evacuate those most at risk).
Nothing stopped anyone living in a low-lying area from leaving on their own, I assume?