Intentionally losing the game or hurting your teams chances of winning(even if that team is just you) is gamethrowing.
Example1:
A Mafia member dies and in his last will he reveals the names of all the living Mafia members. If those names are true then you are gamethrowing, if they are false then you are not.
I'd reccommend changing it to be against the rules even if they are false. Because even if you're not explicitly gamethrowing, you're still leading the town to believe that you have gamethrown and broken the rules, which shouldn't really be an acceptable tactic, because it
1. Makes real gamethrowing more palatable to other players
2. Causes players to report what they think are genuine gamethrows
3. Makes genuine gamethrows less obvious and harder to report
4. Isn't really a fair tactic because it's abusing the system outside of the gameplay (metagaming)