When I get really serious about searching for obscure Chinese poets, I always seem to find something unrelated but nevertheless fascinating at idiocentrism.com. This time it was the Sheng-wu Ch'in-cheng Lu, "one of the primary texts on the life and career of Chinggis Qan". Here's a short extract, plus longer footnote:

Galloping their steeds the charging army rode off.
[At this time our forces had a man named Taqaiqa in Jamuqa's army.] The Emperor’s Jeuret follower Cha'u'ur was his relative and went to visit. They happened to be riding together. Cha'u'ur did not know about the plot. Taqaiqa tapped him on the side with his whip. Cha'u'ur looked back to see Taqaiqa looking at him. Realizing Taqaiqa wanted to say something, Cha'u'ur dismounted as if to urinate. Taqaiqa then told him about the river covenant, saying, ["The situation is now critical. Where are you going to go?" Cha'u'ur was alarmed; on his way home, he encountered the Qorula Yesügei. He told him about the situation and was going to go to tell the Emperor.]
NOTE: The first two sentences could also be "...the charging troop rode off toward our forces. There was among [Jamuqa's] troops a soldier named Taqaiqa." (This would have to be the translation if the Chinese verb fu requires a destination.) I have chosen this version because I do not believe that Jamuqa's troops went off directly to attack Temüjin's forces, but rather to gather their own forces for the attack. If they had attacked immediately, there would not have been time to warn Temüjin. (A few lines further down we see wagon-yurts on their way to Jamuqa's camp, indicating that Jamuqa's force was still assembling.)
It is my interpretation that Taqaiqa was either unwillingly in Jamuqa's camp, or else deliberately there as a spy, but could not risk going directly to Temüjin and needed to find an intermediary. When Cha'u'ur happened to come to visit a relative in Taqaiqa's camp (not Taqaiqa himself), Taqaiqa took advantage of the opportunity to get word to Temüjin, knowing that Cha'u'ur was a supporter of Temüjin. "As if to urinate" is Wang Kuo-wei’s interpretation.