I hate these long range contacts. I rarely find them!
I always assumed they were radio'd (I know that was not a real word) in from other subs/German sympathetic merchant vessels. (at least in an immersion sense)
From a game context, a game based on scripts and RNG's,
I am just trying to figure if they are real or thrown in there to annoy you or have you sail full on towards a ghost that changed course (or made port, as I love trolling the English coast) 3 hours before you arrived.