Given the number of different message apps there are in the Play Store you will be lucky if anyone can answer this (search the Play Store for "message", "messages" or "messenger" and see how many results you get - and that's before we consider apps like Skype that aren't primarily message apps but can receive messages too). All I can tell you for sure is that it's not one of the better-known message apps, and that unless someone who uses the exact same app sees this it's unlikely you'll get a definite answer.
To be honest, your best bet if you really want to know is probably to ask them.