"The cooking technique used." She wouldn't point out the difference if she didn't know what it is. "Soup is things boiled in broth, stew is things cooked slowly." Then again, does he need discernment when he's got her around? Maybe it's not a lack of knowledge on his part so much as efficient resource management.

"Oh yes. It was dreadful. It's really reminded me why I'm such a homebody." Enjoy the teasing, grandpa, you've earned it.