When she told him about having a son he nodded. He knew she had a life before him. Just as he had a life before her. He would be a stepdad if the child ever came to the island. That scared him more than becoming a father in itself.
He thought back to Westeros. The captain's daughter on the ship back to the Iron Islands... the one that had wanted to be his saltwife. That was the only one he could think of that might have given him a child back home. So the way to not think about it was to tell Aurora what he was thinking. "There is a chance I have a child back in Westeros too. I know for certain there wasn't one at Winterfell. But there might be one... If the child and it's mother survived the war and/or Euron."