Having left Mui to continue exploring the forest close to the entrance of the mystic realm on her own, Mui didn't waste any time as she happily made her way through the forest in search of more Nascent Soul Realm demon beast to hunt down and spiritual fruits for her to eat. Having grown fond of this kind of lifestyle of fighting and eating delicious spiritual fruits after the few weeks she had spent training with her master inside the mystic realm.
At the very least, for the foreseeable future, Xuan Hao wouldn't have to worry about Mui using her time on something other than training.
The only thing he had to worry about after leaving Mui on her own to explore the forest at the edge of the mystic realm was when she finished exploring the forest and began moving deeper into the mystic realm.