Lex recalled everything he had heard at the Inn about the 'alien invaders'. A lot of people who faced them called the aliens, while a lot of people claimed to have fought some kind of robots. The assumption he had made was that the invaders consisted of a race that also used a lot of robots.
That was a concept that was easy for him to understand. But this robot having a wisp of a soul inside of it confounded him. Especially because… he was the one calling it a wisp of soul. In fact, he had no idea what it was.
Looking at it, his intuition told him that it was a sort of mirage of an actual soul, but the soul was not present in the robot's body. Instead, it was somewhere else, and was using the wisp to remotely control the robot.
Of course that was only a guess and could not be confirmed, but Lex more or less trusted his intuition.