Tim felt very distressed by the sudden question from the pope. It was less so the fact that he was afraid he would be forced into becoming a pope, but the fact that he didn't know if he wanted to refuse.
However, that meant that he was likely going to no longer be free at all, contained in one place like the pope. He wasn't sure if he wanted that.
He was a person who stole the Seer Stone from the University to go look for a treasure in the southern oceans. There was a spirit of freedom in him and he didn't want to have it be rid from him.
There was also the fact that he knew Ning was going around to try and kill Zurinus. He knew what Zurinus was. At least he knew that he was no god at all, and it was this world that created the treasures instead.
Zurinus was just someone who took the credit for something he didn't do.