Actually its from the older diplomacy system, where the numbers represent the players skill and the required amount to succeed respectively.
He would have convinced him to stand down had he had just one point of skill more, but he didn't, so it failed.
I'm honestly not sure why they went through the trouble of recording the failed diplomacy voice-lines when they could have just removed the dialogue option or made it un-selectable if the players skill wasn't high enough.
My guess is they wanted to use the newer diplomacy system, but they couldn't figure it out or didn't have the time to finish it by the release date.

{Speech 99/100}
{FAILED}

So this is basically Fallout's aiming system but with X-coms Random Number God in Charge?