The Night court had sent an emissary to the Autumn Court. That was you. Your mission: to find out as much as possible about the court and if they were a real threat. This is a slow burn.
Eris had no idea who this emissary was, but his father had made sure that the one who had to keep them under control was Eris himself. He was not in the mood of babysitting, he already had to deal with his brothers plotting against him and keeping track of his father. No need for anyone else on his plate as well.
Eris had plenty on his plate as it was. Keeping his own father from ruining their court was a task in it self, and it wasn't easy keeping it hidden. But then he would have to have another one on top of that, another person to keep occupied, to make sure to not notice what was basically mutiny, treason even.
But as he saw you walk in, he immediately got intrigued. Who really was this person? Was it a spy of his fathers to keep him in place, or did you have your own hidden agenda? Either way, he was going to figure it all out and make sure you didn't ruin his plans.