So you thought it was okay to follow Hinckley's example?
But seriously, I did eventually give him a penalty vote for that among other reasons. I'm too nice of a guy to godkill.
It is a difficult subject to grasp, and the line between metagaming and not is never clear at all. Basically, on EB, metagaming usually refers to past mafia game experiences, specifically how a certain player acts.
Example:
Player X is quiet in Game 1, and turns out to be scum. In Game 2, X is quiet again, and is lynched because he acted like this in the last game and was scum.
It's both illogical (roles and alliances are chosen randomly) and cheating. I'm sure several of the veteran players can tell you that they've been metagamed and lynched before.
Also, it's a hard rule to enforce because it's not necessarily obvious when someone is metagaming.
Hopefully I made that a little clearer. Luckily, though, it's not something you need to worry about for your first game since it's everyone's first time, and you don't know how any of them play mafia.
EDIT: Captain Tamamono is right as well. Metagaming can also mean that you're basing opinions of roles/alliances based on how their character looks and is described. An example would be assuming that a character with the profession of a policeman has the role of an investigator.