Although Joshua did not like to play tricks, his EQ was not low. The warrior clearly knew that the old mage would invite him to travel together over to the Imperial City. Other than sincerely wanting to help the warrior, part of it was because the old mage wanted to strike an impression on the people in the Imperial City.
The current political situation in the Imperial City had yet to become complicated. In short, there were only a few parties such as the Central Royal Family, the local nobles, the Church and the more powerful merchants. The royal family had obviously suppressed the other parties because they had the emperor who had the strength of a Legendary tier. However, even in that case, there were many smaller factions under each party. Some of them even joined forces with the other faction in other parties just to for their own benefits.
Meanwhile, that sort of things was actually not uncommon.