In the states y'all is a southern expression used in the southern states almost exclusively. It just surprised me to see it used in this instance. Y'all have a nice day, hear? South.
It's just an accepted option ;) Well, we write "you all" but the algorithm may shorten it. If it helps some people distinguish "ty" and "wy", why not accept it. We also accept "you guys".
If this were a question, would the only difference be the intonation and the question mark?