Why is it called grandpa in Mulan Poetry?

According to relevant research, southern dialects contain a large number of ancient Chinese pronunciations. For example, southerners often call their father "Ye" and grandfather "Dad", which is contrary to modern Chinese. This phenomenon was caused by various wars in ancient times, and a large number of people moved from the Central Plains to the south. After they moved to the south, they still maintained their original traditional customs and culture, including the pronunciation of the language. Different traditions maintained by immigrants in different times have resulted in the characteristics of southern dialects today.