He probably killed a grayling. Base raids specifically target you, then livestock/gardens, then structures. If you put up high walls so that enemies can't see your livestock/gardens they won't get attacked. Trolls can see over high walls and they can throw rocks and break even stone walls but if you put a roof over your livestock the attacking creatures can't see them and won't attack them until after they poke a hole in your structure(s).

https://steamcommunity.com/sharedfiles/filedetails/?id=2853688746
https://steamcommunity.com/sharedfiles/filedetails/?id=2857321032