Published Means Perfect, Right?: Dialogue Failure

Recently while reading one of Lillian Jackson Braun's great books, The Cat Who Knew Shakespeare, I stumbled upon an error that I believe can be a very instructive example. Read this short piece of dialogue between the two characters and see if you recognize the the odd error.

"Jody thinks it would help if I grew a beard." [Junior]
"Not a bad idea! Your girl comes up with some good ones." [Qwilleran]
"My grandmother says I'd look like one of the Seven Dwarfs."
"Your grandmother sounds like a sweet person, Junior."
"Grandma Gage is a character! My mother's mother, you know. You must have seen her around town. She drives a Mercedes and honks the horn at every intersection."

Analysis
I am not talking about the the use of two exclamation points, though that is somewhat of a problem.

I am talking about the line where Qwilleran says, "Your grandmother sounds like a sweet person, Junior." That makes no sense in the context of what Junior said. It also does not logically lead to the next line where Junior says his grandmother is a character.
Qwilleran should've said that the grandmother sounds like an interesting, funny or astute person, but sweet does not fit here.

I know the error is small, but it distracts. It distracted me enough that I stopped reading and re-parsed the sentence.

Authors who've published 20 novels can afford errors like these, but those of us who are looking to get published cannot. Yes, that's how closely we have to edit our stuff.
It's crazy, but it's the writer's life.
What do you think about it?

~Newton Saber