It was saying that night elves and nightborne collaborate to guide the horde and alliance, in lore they are actually working together, and have the alliance night elf group and nightborne horde group work to ensure the horde and alliance are ready to face world threats instead of destroying each other like Azshara/N'zoth almost manipulated them into, they also work to ensure no Arthas/Garrosh ever arises to use the factions for evil or war. Finally they ensure the horde and alliance conflict doesn't stop them from rebuilding their civilization and forests all which keep getting uprooted and attacked by conflics. Tot hat effect they flood broken isle nightbonre areas with night elves and Kalimdor night elf areas with nightborne.
The Thalassisan elves operate differnetly, the blood elves actually work witht eh draenei, unlike the night elf/nightborne who feel thesmelves far avbove the faction conflict and would rather manage it so that it doens't interfere with more importnat goalls like protecting/defending Azeroth or rebuilding their shattered lives, the Thalassians are more noble minded for peace. Teh blood elves work with the Draenei to help make the alliance and horde find peace. Now nnot all blood elves are on board for this ofc, but enough, and the effort i s lead by Liadrin and Alleria - it involves a complex horde/alliance relationship, and you still have hatreds running between some high elves and blod elves specifically old silver covenant/sunreaver individuals, however you also have those working for peace. this eventually leads to a stalemate peace in Quel'thalas when the alliance armies attakced and the sunwell was almost destroyed forcing the high and void elves leading the alliance, and the blood elves leading the horde to finally come to their senses and agree that for the High home to ever survive, war most never come to it at least from the factions, and so they force a power share betweent he horde and alliance, with the void/high elves representing hte allinace and the blood elves representing the horde, Quel'thlaas becomes controlled exclusively by Thalasisians, membbers of factions need their respective thalassians to agree to them visiting the area, and inter-elf fighitng is strictly forbidden on penalty of death.
This opens the door for a sophisticated cold war amongst haters, but also people working together to forge peace. The lightfoged become pretty friendly with the light seeking high elvs and blood elves, which helps, and they become the main draenei face in the land. While these guys work to finally bring peace between the factions, others continue to try to undermine that and defeat their opopnents, this tug of war is how the balance plays out.