The old man knew that there was no fixing of this mistake. His people are already gone. They are nothing more than mindless servants of the horde, warriors to be used on the frontlines against the myriad races they will be ultimately used against as nothing more than tools for slaughter.
Nobody will remember their history, their struggles, and their victories. The world will only know that they were bloodthirsty, violent monsters, invaders on their 'peaceful' land, trying to take their life and the world itself away from them.
They will only know that they were the demons, the brutal monsters, the violent beasts that were nothing more than bipedal pigs.
A completely twisted joke on their legacy. They had so much more to give, just like every other intelligent species they also had their own history, their own unique, special things that could just as easily define them, as to how the future will now ultimately remember them.