My (admittedly) simple understanding:
Buckwheat = black/white = his genes are black/red - he is not pure for dominant black since he produced a red offspring when bred to a black/white
Damisi = black/white - her genes are black/red - she is not pure for dominant black since she produced a red offspring when bred to a black/white.
We also know Damisi can not carry brindle herself.
Sire (Wili) is black/brindle (we know this b/c he produced a trindle offspring when bred to a red dam); Dam (Kimaji) is red.
Wili (sire) can only pass along one of his e-locus genes (where black and brindle hang out) either black or brindle can be passed, not both while the dam passes along her red gene.
If sire passes his brindle gene combined with dam's red gene, Damisi would be brindle in color. If sire passes his black gene, combined with dam's red gene, Damisi will be black (black is dominant to red).
To make the gene pair, only one gene can come from Wili - either black or brindle and one from Kimaji - red and we know Damisi is phenotypically a black who has produced both black and red offspring - therefore we can correctly conclude Damisi is a black/red, not a black/brindle/red.
She can not carry the brindle gene which means she does not have the brindle gene to pass on to her son, Johnny.
The end result - Johnny could be pure for black (one dominant black gene from dad, one from mom so no chance of reds.) Or Johnny could be a red factored black, getting one red gene from either mom or dad. Or Johnny could be a red AND tri factored black, getting one red from either parent and a tri gene from either parent since Buckwheat has produced a tri and Damisi has a trindle littermate.
All that said, i DO see what appears to be brindling in his coat, and knowing basenjs, perhaps they have not read the color genetic pages as we have. Far be it for me to ever say never. Only time will tell, assuming enough of a breeding sample is doen. Fascinating color options, even without the brindle in the mix. Good luck with the babes.