Because they were ALL trying to trick you, and they were successful. All the guy really has to do is post in the main lobby, "it's Marriland come watch me" and he'll get a ton people watching.
Anyway, if you didn't upload the replay, then there is no way to get it back, sorry. Battle rooms expire and disappear after 15 minutes of inactivity, so that means the battle has been gone for ages. If you ever lose the battle by clicking out of it, it's still very simple to find it again. You can go to your browser history (Ctrl+H in Chrome) and find it there, or you can simply hit the back button, which will take you back to the battle where you can upload it.