I am aware of at least two verified instances in New World Cichlids where a presumed male, in isolation, laid eggs and fertilized them (the best known being Ginny Eckstein's "Tootsie", a Caquetaia spectabile). A self-fertilzing hermaphrodite is quite rare, and this is the first time I've heard it claimed of an African species. The condition does not seem to be genetic, as many people got young from "Tootsie", and none ever became like their Daddy/Mommy. Given the known ability of some Mbuna to change sex, it is not inconceivable that your isolated fish simply stopped midway while both sexes were present.
If you can't Dazzle them with your Brilliance, then try to Baffle them with your BullS***!