I've been playing this online mafia game all day and i have no way linked any of my personal details in anyway with it.

So anyway i was on the forum of the game i've been playing and a random person starts trolling me in forum chat. I go along with it and he eventually says "hey [my real name] " how has he found this out? and he also linked a real life photo of me somehow? I think he knows my IP from a server i used to host on the game. Would this of helped him get it? and if so how?
Edit: It definately wasn't someone i know in real life i can assure you