It's part of the Special's job and skill set to be good at deciphering topography. Not that one would have to be in order to understand Arthur's non-verbal communication. Powell's own look and brief tip of the head may be taken as acknowledgement or more accurately as don't be stupid. The politics here may be opaque and cruel, but it could be worse.

Arthur should be perfectly safe with his escorts. They have no interest in making his day more interesting. Assuming he has no immediate complaints, the trip back should go without incident. The things he had with him to the Spire will follow some hours later.

After that, transport out of here will be arranged. It will involve a familiar hood and end up somewhere dark and unfamiliar until someone comes to claim him. He has friends. At least one of them will be notified.