Why is my ex acting like a child?

A couple a days ago, we went all out on Facebook saying that he got a new girlfriend and how he's never felt this way before, etc. it was all bullshit and I knew very well. Because it all went down yesterday, deleted. So today, my mother gets a text from a burner number, easily downloadable from the app store, saying that, "did you know your daughter is stealing your car every night and delivering drugs to boys for sex?"