I don`t know if this is just a random encounter or not, but it is already the second consecutive time that, everytime I travel (fast travel) to the Rattay mill, I encounter a man with a longsword, a shield and a full suit of armour asking me for my purse. He has a poisoned blade, so one scratch is enough to slowly kill me, and he is awfully skilled and resistant.
Is this just a random encounter, or does this have something to do with the Delicacies quest given from the innkeeper at the Inn in the Glade? This happened after I killed a wild boar, but I swear there was not a human soul except for me in the forest... even though I can fast travel back to the Inn without a problem.
When he spots me, I also get a message that people will notice if I do something wrong... I killed the wild boar in the forest near the Inn in the Glade, there was nobody around, and I get this message at the mill... this doesn`t make any sense...

EDIT He`s there even if I don`t kill any game!! I`m sure I didn`t do absolutely anything wrong in Rattay, why the hell is that guy there??

Question: did you participate in a tournament in Rattay and win (against Black Peter)? This message is generally displayed to tell you that an NPC is now angry, outside of the obvious situations when you fight Cumans and bandits.

I’ve had it displayed, for example, when Henry was threatened by a bunch of bandits as part of the main quest, he talked them down from fighting and then he found them later, while they were looking for someone, and decided to take revenge, because they were unpleasant dangerous buggers (even if they weren’t after Henry anymore). I obviously didn’t care that they would now hate Henry – I wanted him to kill them all.

There may be cases when this message doesn’t mean you did something “wrong” but rather that you pissed someone off and that person used to be a non-combatant NPC earlier.

Yeah, I finally defeated him, and it was actually Black Peter. Really a sore loser (and I`m being kind). This was the first time ever that I faced someone with a poisoned blade, what the hell.

Indeed. In fact discovering that he kills people who beat him (or, more precisely, killed them before you killed him) is part of a side quest. Good riddance.

Really? How do I start it? Is it too late now?

Talk to the blacksmith in Samopesh.

Before the latest patches you'd need to talk to him to trigger the tournament at all (because the tournament itself was a one tine event tied to the blacksmith's quest). Based on what you wrote I assume tournaments can now be triggered without the quest (because they're a major feature of the newest large patch). I think the quest should still work properly, but I'm not sure (I did it the old way, triggering the tournament by taking the quest)

Yeah, it still works. I found the blacksmith, and the quest was basically solved on the spot. Thanks for the tip ;)