Aggressive adventurer attacks bird in my trap

[PALU]

Sorry for this being a bit rambling, but I'm trying to provide as much context as possible...

It's midnight late autumn, so visibility is zero, i.e. I can't see what's in the tile next to me. I've just woken up and tried to move out to the overmap to continue work on my future farm fields, but can't due to local activity. I drew the conclusion that a bird probably has been caught in one of my "bird" traps and moves to investigate, and I eventually find that there is indeed a bird caught by trying to move into it, but I can't attack it as I can't see it, so I try to light a fire (I don't have any torches). While trying to do so, an adventurer known to roam the area shows up in the distance (by the virtue of NPCs wearing light vests), disappears, and then reappears angry, so I abort my last attempt to light a fire and retreats. He then move up to the trap and kills the bird, immediately after which he calms down. I approach, greets him, and pick up the bird carcass (lit by his light vest).

I don't think NPCs on non hostile terms with the PC should steal catches from traps by killing animals caught in them (he didn't steal it strictly, as he had several turns to pick up the carcass before I reached him, but didn't do so, but still).