Nice clear pictures ... your water parameters appear to be great!
I agree, looks like a wound of some type, you don't see them often on the operculum not much flesh there, keep an eye on it. If it starts to redden up it means it is starting to get infected.
Can you isolate the fish? Africans as with most fish will pick on any fish that appears weak.
I keep a couple small volume tanks ready for that purpose and have brought a number of battered fish back to health that way. I have also used/seen breeder boxes clamped or hung on the side of the main tank for the same purpose.
If you don't have one you can DIY a cheap one by buying a 2 - 3 gallon clear plastic tote at a Dollar Store, Walmart or Canadian Tire. Drill a bunch of 5 mm (1/4 in) or less holes in for flow / circulation and clamp it inside your main tank.
If the holes are small enough it can double for brooding females holding eggs in future.