This chapter is completely recontextualized if you read chapter 9.
The reason he is so overprotective and snooty in his sister's business and why he even says that he will find the crow that stole her money in the next chapter is because he believes it's his duty to protect his family now that he's the man of the house. It's actually quite sad.
Haha, asking if she had a wet dream and gone before she could even make her attack. He's skilled in the art of younger sibling annoyance-fu. His heart beats to the tune of "I'm not touching you."