What was happening when we did the mission for the first Seed of Light?

I usually only use one character, a hunter, so I thought i would try making a secondary character(a warlock) and did the fairly short grind to unlock the seed of light on him, and started wondering during the mission; What was happening to make what we saw happen? I’m not sure if i missed something, but why does the Traveler only speak to us in that mission? Is it because we are a “Chosen One,” or is it just plot convenience for the new subclass?

I believe it is because we are the “Chosen One”, as we answered the call of the Traveler in D2 Vanilla.