I love Harry and Ron moments! It's a very good moment between the two of them! Even with it not being in the book, I think it's fair to say its something Harry would do, I think it's the movies way of doing the scene in the book where the trio are in Ron's room and Harry tries to convince Ron and Hermione to stay while he goes and looks for the horcruxes.
"Don't tell her I said that" I love Harry shaking his head like "Yeah, yeah I know."