However, when you mention that this boy is honest, you may mean that he doesn't change wallpaper often or feels comfortable with wallpaper that is too exposed or sexy. So, maybe it's because he thinks this beautiful woman is beautiful, but he doesn't want to hide or cover up this wallpaper.
In addition, it is also possible that the boy is just curious about this beautiful woman, or that this beautiful woman is an important person, such as his girlfriend or family. No matter what the reason is, the decision itself has no fixed explanation, and the specific reasons need to be determined according to the specific situation.