Note the lack of blood, compared to the last time we were shown such a scene. Good odds this was magic, which likely only the royal family and may be a few select others really have any chance of going against. Basically, it's like beefing up your physical security, and then getting hit by a hacker. If this was magic, it wasn't necessarily something they had expectation to be prepared for, or even necessarily the means to meaningfully prepare for (as the only sign of mages we've seen thus far outside of Arcus has been Hyperion's royal family, implying that it's rare and privileged to possess magic outside of Arcus).