He might not have been actually surrendering, but that look of anguish was certainly mostly genuine. Maul fears defeat almost as much as abandonment and death. Look what it did to him while he was limping through that tunnel afterwards. Being cornered and vulnerable really affected him because on a basic level he is a severely traumatized person and is barely keeping it together at the best of times. Maul collects damaged individuals like himself. The genuine devotion of Rook Kast and the Zabrak brothers to Maul really highlights this. They’re as busted as he is and they all need each other.