Welcome to Springfield Heights

I'm sorry if this has been asked and answered, I try to read all the posts in all the threads, but I might have missed it:

It's my understanding that all agree this is not an event, but an expansion. I'm still fairly new to the game (and this forum), so I haven't experienced an expansion "live" before. If this is not an event: Why is there a leaderboard in the friends section? I've only seen this during events.