This question involved some of the plots and character settings in Hua Qiangu's novel. In the novel, Tang Bao and Dongfang Yuqing were both Hua Qiangu's companions, and Tang Bao was set as a child in the novel. Therefore, he called Dongfang Yuqing "Dad" may be an intimate expression or to conform to the language habits of children. It should be noted that different novels may have different plot settings and character settings, so the same character may be called differently. For example, in some novels, Tang Bao might call Dongfang Yuqing "Grandpa" or some other form of address.