@viovee pretty sure they were already thinking about naughty things before that (when they were surprised he was there when she received the letter after midnight) so yeah, her tying a ribbon on him seems a little bit endearing to me but not really that naughty, though it feels like they kinda interpreted it that way
After reading the other comments about the ribbon comment.
Imma think-
The mom misunderstood so bad she thought he meant a Ribbon Collar, like one of those cute kitty collars with ribbons on them, thats the only reason i can think for her to be so shocked XD
I need more screentime of little brother ♥
it is incredibly ridiculous how innocent the duke is but even little brother can hear the double meanings in what the duke is saying