Are "truces" considered cheating?

One of the enemy team thanked a member on our team (the guy with the most kills, but extremely selfish) for the truce they both had. I remember our guy running away from someone who had a lot of damage, and didn't know why at the time. I think it happened a couple of times. The guy on the team was support and pretty weak.

Wouldn't this be cheating? How do people who admit these things in chat, especially when the stats show they didn't kill each other, not be banned?

Thanks for the help.

Edit: Just to clarify, our guy was extremely powerful and a delete button and went something like 17-5-2, the other guy was a support and went 2-8 with only 8 assists on an enemy team that had over 60 kills.

Our guy was top, the other guy support. Now that I think about it, three of four of them would come exactly to where we were even though there was no way they could have known. If I said I was going top, all of a sudden, the enemy would be waiting for me and pop out of a bush when there was no reason to have known I was going that way. One instance, I specifically said that they were all bottom and we needed to push top. I went that way and they all came out of the jungle and killed me under my own tower.