Michael didn't expect the people from Nest to be so talkative, but Eren told him a lot. He explained various things that didn't make any sense at first.
That was also how Michael learned more about the Nest's hierarchy, how many Curse Users were at the Nest, how strong they were, and some neat information about their training methods. He was not sure what was going on, but Eren seemed to trust him a lot. That didn't surprise Michael a lot. He felt that he could trust Eren as well. It was weird.