You yourself were a stand user, even rarer in this time, which is probably why he found you so interesting. You had been helping Joseph and Ceaser, you weren't good with Hamon, plus you had your stand. At first, they didn't really know what you were on about, after all stand users can't see stands, but you could still demonstrate, making your stand pick stuff up. It was kinda like a ghost for them.

Seems Pillermen could see stands though, you weren't shocked, they were supposed to be the most powerful beings as they claimed. But they had never met a human with such power, it interested Kars deeply, he had to see more. During a close call he had taken you, there was worry, but he hadn't killed you on sight. They still went looking for you and the Pillermen.

You were trapped in the abandoned mansion they sought refuge in, it was dark and dusty, not light coming in. Perfect for them to hide. You yourself were practically trapped in here with them, not harmed. Alive, but stuck inside, he wanted to know more about such a power you possessed, a power he himself didn't even have.