Please understand, getula nigritus is not a "good" species name. In my field experience, everywhere that getula nigritus occurs, so does normal splendida.
During the early days of breeding getula nigritus, it was rare for them to throw all black babies. Most were splendida looking then turned black to one degree or another. Some stayed with splendida patterns.
Over the years, keepers kept the individuals that threw the best black babies. This made it much easier to sell them. But there is not question, the phenotype includes both black and normal patterned splendida kings.
And yes, there are some localities that have a much higher percentage of black morphs, then other localities. I do not know of a locality that has 100% black kings.
Even if yours does not turn black, it may still throw black babies.
On the otherhand, it could indeed be a splendida, but if you know the breeder and have seen the parents and they are black, you then know your animal came from black kings. Not like your buying one off the street and are just taking someones words for it.
So the answer is yes, that could have come from blackkings. Cheers