You're correct but you have an off by 1 error.

First, the genie grants the wish.

NumWishes=0;

Then, having completed the wish, the genie deducts that wish from the remaining wishes.

NumWishes--;

And to complete the thought,

Lastly, the genie checks if the lampholder is out of wishes

If(NumWishes==0) {...}

(255==0) evaluates to False, so we fall past that check.