Guild Wars 2

this guy climb over the wall into lowland keep.. obviously lowland is not breach.

That looks more like he “bugged” into the wall. This happens to me sometimes in ini’s when I am standing next to a wall and use an attack that teleports me to an enemy. All of the sudden, I am stuck in an object, wall or below ground.

There are underwater entrances into that Keep, it’s possible you’re targeting him inside one of the tunnels that leads up into the wells inside the Keep courtyard.