They're probably going to integrate elements from Zenly into the main Snapchat app is my guess.
I can't see how 2 million users are worth it either. It really isn't even that many anyways because I'm sure many were already snap users)
Unless it's because they really wanted to do Snap map and are basically paying to have a fast implementation and have that many people with it enabled from day one. This way when Instagram copies them it will take a few months.