No I think its a thank u for taking care of my child. Cuz if u put the pieces together. Hearang might be a child adopted by mook bu* just like the Commander when he was a child. cuz as it said in the prev chaps if a fox birthed a boy they will handed to the wolf, and since the herbalist is a freeborn he might have no idea of what happened inside the fox territory that his wife came preg.
And as the mother also mentioned in prev chapter she said to take care OUR son or something to the herbalist.