I would advise we go peacefully.
I took a further look at the save.
No one's score went up this turn other than Vox. We know they got Polyth for sure on that basis. The culture graph should show it starting next turn as well.
The land area numbers tell us, or confirm for us, that Vox is coastal (we have 1.97% of world land area, they have 1.00%). They don't have many land tiles. They are at the end of the river, but which end? I doubt it is the tundra end, since this map was vetted, but we shall see.
Contact is likely established by their scout moving in and out of view. A good move since it keeps us in the dark about their whereabouts longer (you can't rush what you can't see).
I should send them a greeting sometime later today. Anybody have anything they desire communicated?