Scout Ben Clark informed Custer that 150 warriors were in the village, many having been involved in the Solomon River massacres. Custer’s surprise surely caused the death of most of them.
Black Kettle’s camp was the entry point for the returning warriors and they may have stopped there before moving on downriver but 150 warriors would have put up a much stiffer resistence. 150 is way too many for the overall size of Black Kettle’s camp. Even Custer didn’t claim that many killed and he was prone to exaggeration.