We can usually understand how or why a note came to be on a receipt. Whether it's a joke, an insult, or a general observation, there are many reasons why you might want to use a receipt to communicate. We can't make head nor tail of this, though.
Apparently, whoever served this customer does not yet produce milk. We think it's unlikely that the customer asked them to, and they clearly provided some milk anyway. Why would anyone feel the need to print this? It's bizarre!