Yup. The full name of the converts is xxx ben
Avraham avinu (xxx son of
Abraham our father) or xxx bat
Sarah Avraham avinu (xxx daughter of
Abraham our father).
The "xxx" is very often
Abraham and
Sarah.
Female converts will also have another name: xxx bat
Sarah imenu (xxx daughter of
Sarah our mother).
It's not surprising. Jewish women have two names: xxx bat [name of the father] and xxx bat [name of the mother].
A man who would be called xxx ben [name of the mother] would be the son of a Jewish man who converted to another religion or a bastard. It also happened a couple of times in North
Africa, when the parents were divorced and the son clearly sided with the mother.
I hope it helped!