He's cleared of conducting Secret diplomacy, as stated in rule 2:
"Any form of diplomatic discussion between opponents must be posted in the game chat in English or in a language that all opponents understand. Diplomacy includes, but is not limited to: proposing truces, negotiating alliances, and coordinating assaults."
Asking for a truce or a coordinated assault IN game chat is not against the rules.
God, grant me the serenity to accept the things I cannot change,
The courage to change the things I can,
And wisdom to know the difference.