I was thinking about the Vex. When I was reading the Grimore cards about them I turned my eyes the Vex Precursors. They speculate that the Precursors are ancestors of the Vex we fight today, but what's interesting about them is their appearance. They appear as if they were forged in light. They are mostly white/silver with gold on them and have blue eyes instead of red. Also what we know about the vex is that they predate humanity by eons. Perhaps the traveler visited an ancient race and they built these machines similar as to how us humans build machines, to protect and fight wars and maybe eventually the machines went rouge and destroyed their race long after the traveler was gone. This would also give us some insight on how these aliens may have looked like because when humans build sentient machines we usually make them in our own image. Just my input on it. I could be wayyyyy off or very close.