There is the hypothesis that quite a few lineages and maybe species came about by hybridization in the long distant past when lake levels varied forcing older lineages together.
Not sure at all about this one, it is the first I have heard of it being from those two types but then I know very little about Tropheus sp "Red Belly".
I think in the wild Tropheus types are quite resistant to producing hybrids that go on to breed and form new types. As shown by this study.http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1560039/
Even when they are forced together in the wild by man.
But then there is always the exception to many rules.
If you look here http://www.biomedcentral.com/1471-2148/7/137
Fig 3 then you can see Red Belly falls within AFLP 3 along with the ones called Tropheus sp."Black"
But in fig 2 the mitochondrial DNA tree most of those tested fall with moorii types but one falls with the sp. "Black" types!
Evidence that it is hybrid? I guess a special study might give a clearer picture.