They were just in the same club. Maybe it's hard to believe but they do have similar taste/interests afterall (they were together few years ago, hellooooo). So it's not surpising that they visit the same places.
Rihanna what a mess is this? I wouldnt wantt o be associated to Chris in any way specially after that mess of song he did a few weeks ago, she should stay as away as possible from him. And a majah side eye to TMZ for putting that banner on their site : Rihanna and Chris Brown - Greatest Hits.