Is this a new word?

Ash • Wife 💙 Mommy to a little boy as of 3/17! 😍
Mines? "That's mines." Or "I found panties in my house that's not mines." And they use the word over and over so I'm assuming it's not a typo? I understand this is an app to conceive babies, but "mines" sounds like a word used by babies. Beyond ignorant sounding, this one takes the cake.