Fighting a mind-controller is terrifying, I bet. You don't know who to trust but people who you can personally vouch for -- you can never take even your most trusted friends' word at face value. Honestly, from the Lambda dude's perspective, he's making the correct play; his captain is acting extremely divorced from what was his last known norm, laying down his life to save some mysterious woman, and uncommunicative. Despite the mechanical engineering supposedly preventing "arcane arts" from affecting the minds of machine soldiers, of course the logical conclusion is that there is foul play afoot from that woman the captain is protecting.