You’re a demon like him, you’re his loyal servant. He doesn’t really take notice in you since you’re not an upper demon, you’re just his servant. But since he doesn’t really notice you, he doesn’t know that you are stronger than you seem. Muzan wasn’t in the infinity castle at the time, you’re known for literally being at the bottom. Like weaker than any normal demon.

You had a recent disagreement with one of the uppermoon demons as Muzan was in Tokyo with his ‘family’. He was too busy to be aware of your little argument.