This karma does not refer to how many people the Demon Race has consumed, but to how much blood food has been eaten. Whether it's humans or other demon races, devouring will lead to culpability. The Da Xuan Dynasty is not rigid to the point of saying that no karma can be involved at all, as even human cultivators have quite a bit of karma in themselves, let alone the Demon Race.
So those who can meet this requirement are mostly local demons of the Da Xuan Dynasty. Most of them have to rely on their own cultivation and hunting wild beasts to survive, hence their karma is at a lower level.
Mao Shijiu is uncertain whether the karma within him is qualified, so he lacks confidence.
After all, he was born in the Demon Domain. Although karma can be reduced, without a way to measure it, if he goes over there and his karma exceeds the qualified threshold, he may be killed as an Evil Demon.
