Why is the river god of Heishui River called Tang Priest and Master?

Honorable address In The Journey to the West's sequel story, the river god of Heishui River was honored as Master Tang Yan. In The Journey to the West's sequel, Black River God, because Jiulong, the nephew of the West Sea Dragon King, occupied his daughter's house and the house of Black River God, one day, Tang Yan and his disciples passed by the Black River and told Tang Yan the truth. Tang Yan asked the Monkey King to seize Kowloon, but the Monkey King could not fight. Then, her daughter cast a spell on the Tang Priest's disciples to cross the river.