The Chosen - When are they supposed to appear?

[Dr.Cthulhu]

I recently started a new game on the beta branch. Around 2250, I found a wormhole system, but didn't have the scientists available to survey it. A couple of years later, I start moving some scientists and construction ships in - only for them to immediate be sent MIA and a new empire to show up in that system - The Chosen. They quickly expanded outwards, I'm their only current neighbor, and they've got some pretty hefty fleets for 2260.

I've tried to find more information about them, but other than a very short blurb on the wiki about their home system, there's not much. It says that they shouldn't be developed wormhole travel (I haven't even researched it yet!) until the midgame, and they're supposed to be a midgame crisis ala the Khan, but this seems very early.

I also didn't get any notification or events about this happening, possibly due to not having any intel on the system when it started, but I'm not sure if this is intentional or a bug. They just showed up out of nowhere and took over systems rapidly.

They'll likely declare war on me soon, and I'm not certain if I can win or not. So is this all standard for when they show up, or have I run into some bug?

[Biggs]

i found two empires named "the chosen"
one is a fanatic purifier who spawns in galaxy

the other is an empire i made myself by that name years ago
they are a religious human empire
i made several human empires and 2 vulcan empires
i wonder if any more of my names will show up in stellaris by amazing coincidence

[mss73055]

"The Chosen" appear rather harmless. I never saw them break out yet.
In their current state they're 350 free pops to scoop up. Also there's this dig site even farther out.

[Dr.Cthulhu]

I managed to fight off the fleets (each fleet was about equal to my own, but they split up to conquer different chunks of my empire), but without wormhole tech, it's only a matter of time till they build up and return through the wormhole to fight again. So right now I'm trying to shore up defenses for their inevitable attack.

It's cool and all, but, seriously, are they supposed to show up so early, with no warning? I've tried reading through the event files (I think it's the first_contact_dlc event file), but I can't really tell what the prerequisites for it all is.

The amount of research and materials they have in their little cluster is big, and I do have the difficulty turned up (Commodore, I think?), so I'm wondering if that boosted their research and allowed them to come through early, rather than them unlocking wormhole travel through an event like I previously thought.