Rio de Janeiro
I think it makes sense not only iconically but also thematically: when you first encounter Leam he just got washed away by the sea and needs to rest before he can help you; but in the next adventure you know him and he's already rested, so he's more readily available.
Yes, the thematic explanation occurred to me. I just don't understand why not place the card straight at the end of the row with "A Castaway" side up in the first adventure, instead of creating an exception to the rules. It's not like it would terribly unbalance the adventure, considering that the rulebook suggests playing without one or both ally cards if you find the game too easy.