Have I Found The Most Rarest Train Set On Sehs

So I was waiting at Ashford for trains because I’m doing a bit of train spotting and I saw a southern class 377/1 to another 377 and Joe Burgess did that in BML so have I been the first to see that https://www.xbox.com/play/media/EKEUDS4N that screenshot is my proof of seeing it

 

Genuine question as I’m a virtual train lover rather than a real life spotter, what makes this rare?

 

Yep gonna have to explain this one to us.

 

I’m going to make an assumption on what this is, as someone not too knowledgeable with British trains. This is either:

-An insanely rare Southeastern service that happens to use two Southern 377s, which I think they actually have a couple of

OR

-A Southern service to Eastbourne represented by a pair of 377s, since the Class 171 does not exist in TSW