I am confused.

So you had a 4 day (2 week deposit) held from these people but they are only going to use 3 of those days?

And you reminded them that they have 1 more day as per the deposit and offered them to use it?

If that is the case and you offered then you don't have to reimburse them. You could - I don't think most people would - but you don't have to and if he being rude about it then I wouldn't