After claiming control over the Elven Synchronized Intellect Nation (SIN), Xi Wei was playing with it without restraint like a child who just got his hands on a beloved toy.
To put it in Xi Wei's own words, 'a fantasy world without floating island or hanging cities are hamburgers without lettuce'—once that was accomplished, he found that he had gained some extent of Authority connected to 'skies'. He thought about it, and decided that Gaim taking to the air was perhaps a sign that his believers had been free from the shackles of the earth, and as such gained Authority in that aspect.
While there was not telling if that was the actual case, gaining some Authority out of nowhere was not bad.
In fact, Xi Wei was very thrilled.
It was worth mentioning that Zothor, the God of Sky and Thunder and one of the Seven Divine Fathers held the Authority over the skies. There was no telling it he sensed that Xi Wei had stolen a part of his Authority…