I'm like…90% convinced it aliens. The timescales match up. Nearest star is like…100 ly away? So speed of light that's 100 years, lets assume .75c, and then a ton of speed up and slow down time we're looking at like…500 years travel time, 1000 years round trip.
So if we have ET events, they're going to be so few and far between as to basically fall through the historical record unless it's seen by enough literate people (cough 1500s nuremburg cough)
Theory 1:
What if a bunch of aliens realized their planet was dying, and so they rapidly fled to colonize other worlds. They realized that their genetic code was flawed, they had killed themselves, so a few of them tried to recreate intelligent life, but in a better way, and that's us.
Theory 2:
Life was uplifted on earth with a poison pill. If we got too smart but refused to get along and coexist we would kill each other, but if we managed to remove the poison pill we'd demonstrate to the galaxy that we're capable of cooperating and not exclusively violently resolving disputes.