Simple you were lagging in match after match ruining the game for others -blam!- you. These reports built up until your account was flagged for investigation by Bungie staff who found reason to issue a stand alone warning. For whatever reason you ignored this warning and carried on playing ruining more matches for others who also reported you and earned you a second investigation. This investigation found reason a second time to issue a warning but this time Bungie added a 2 week pvp restriction as incentive for you to fix the issue and to protect other players enjoyment of the game. Use this time to sort out your Internet connection or next time Bungie has to step in again the pvp restriction is for 2 months.