What is the meaning of their saying: Al-Kufi is their Mawla?

"Al-Kufi": An attribution of a person to the city of Kufa, meaning he resided there.

"Mawlahum": He is attributed to the mentioned tribe or people due to wala' (loyalty, specifically through manumission) and not lineage, as the Prophet, peace and blessings be upon him, said: "The mawla of a people is one of them."