
I might be wrong about this, I dont have the materials to test it. But it looks like this already built palisade (claimed) was destroyed by a bug. The raiders seemed to have built another cornerpost by the corner of the pre-existing wall, then destroyed that and by doing so caused cascade damage to destroy the existing wall. I might be completely wrong about this assumption though, I was told by the people that were raided that the palisade was sealed and that the raid happened faster than a 10 hour period.
Another possible thing that could have happened is that the corner post was unsealed and the raiders just extened it one tile, however this shouldnt be allowed imo because you arent allowed to build walls on others claims. This is technically off the claim however it was abused in a way that seems unfair.