The person who said it is Phyonius the Sage, the Elder of Humans in the Era of Change.
In the Era of Change, humans started to use natural resources to build the city of Leyton and destroy the wildlife for food. Every year, they kept going deeper in the nearby forest, but after some point, the visitors of the forest started to see engravings on the trees, they also felt like someone or something was watching them when they went there. After some time, less and less humans started to go to the Leyton Forest, when Elder Phyonius heard about the rumours, he formed a special armed detachment to send to the forest to get provisions. The detachment went there and came back without any loss, they also didn't have the fear of someone watching them. In time, city life returned to normal. Then, one night, when the city doors were being closed, one of the guards saw some strange creature who turned out to be a human guard called Letzest who was sent into the forest earlier that day. He was talking gibberish and his armor was covered in blood. The rumours quickly spread across the city, the city council was gathered, when they questioned Letzest, they found out that most of the detachment that was sent with him was probably dead already.
According to his story, the detachment went deeper into the forest than usual, they came across a lake with a deformed tree in the middle of it with its roots emerged to the surface, making small isles. Humans decided to camp there, everything was good until Letzest tried to chop up a stump, when he hit it with his axe, the lake raged and formed a wall of water, then destroyed the camp, the tree turned into a yellow tentacle and took every human in the lake. However, Letzest didn't remember when he regained consciousness after that, neither did he remember how he made it into the city. Hearing this, Ander the Councillor suggested they should burn the tree with the recently discovered flammable liquid, a detachment of archers were prepared and sent to the forest to do so. Ander returned to the city without others and told everyone the cursed place was destroyed. But the next day Leyton woke up with the sounds of drums, everyone took their weapons and detachments were prepared and sent to the city walls, archers took their places in towers and catapults were prepared. They sighted warriors with longbows and dark armour approaching.
That very exact moment was when aforementioned "It's Dark Elves" line was delivered by Phyonius the Sage. After this point comes the next part of the story:
When elder told them that humans want to live in peace, disturbing and beind disturbed by nobody, one of the dark elves told him it was too late for a peace deal since the humans destroyed the sacred tree: Zorgal Mitael Latunakhe, the heart of the forest. Now the forest was dying, so were the Dark Elves, but they were not going to wait for their end, instead, they'd end the humans first. Without letting the Human Elder talk, they shot an arrow which hit Phyonius in the chest. A war broke out between humans and eldives, Ander, being the only one left from the Council, took the command and ordered everyone to hide in the towers except catapultists, he planned to destroy the elves just like they destroyed the tree. Dark Elves started to cast spells to attack the city, Ander gave order to open the city gates and the humans began a cavalry attack on the elves. Then, he ordered the cavalries to enter a ravine to the east. When the surviving elves followed them in there, the catapults in the city started to shoot fireballs instead of stone. The flames of the fireballs spread everywhere, the elves found themselves in a chamber of fire. Ander and others died in there.
The Elves' attack was repelled, however the city didn't turn back to normal, in a decade, the Leyton Forest just melted away. The ravine in which Ander and others died, was named Death and it was growing, so humans evacuated the city and headed west, there they founded the city of Basturiongrad. Now, in the place of Leyton city there's only Death Vale, in the place of Leyton Forest, there's a plateau.