Questions kinda concerning balance/rank

ViciouscirceBU

I've seen alot of higher rank survivors (11-1) playing with 1 really low rank survivors like 20-14. Me as a seemingly never changing rank 14 killer have wondered, is this a strategy/ploy to get easier killers. My last match was against a level level 7, 1, 11 and a level 20 they were cross play players so I couldn't tell if they knew each other or not. it's so hard to tell what platform they're playing on.

(Side note)How do people tell what platform someone is on anyways I see so many post about PCvs Console. But I thought cross play was for all platforms to play together so how do they know