Loot is likely generated the moment you pick up the container into your inventory.
Because the weight of the container reflects its contents.
So if your lucky charm char had picked them all up first, they would have better items inside.
In terms of area loads, not quite right. Lucky Charm is rolled when you first access (open/pick up) a container. The contents themselves will remain static if you load a save right before triggering but the individual stats differ (so you could save scum to get a better roll on a specific item type). If you open another container (or trader) before opening the original container, the item will now be a different type.
