If you make a wish, it’s true that you have made a wish but the wish itself is neither true nor false. Try to imagine how you would react if, when you said to a friend “I wish I had a $1,000,000” your friend said “That’s false!” If what your friend is denying is your making of the wish, then he’s wrong; if, however, he is trying to deny the content of the wish, then his denial makes no sense.
If you say “I dislike broccoli” and your friend says “That’s not true” he may in fact be wrong in his assertion (the kind of relevant evidence here is his having seen you eat broccoli on many occasions, smacking your lips as you did so and saying things like “Mmmmmm, delicious!”) but, right or wrong, his denial is meaningful.
I hope this helps.