Headcanon: Andrew calls her Hermione in a joking way, but he knows that Alice totally takes it as a compliment because she really is very much like Hermione. He knows that Alice thinks Hermione is accomplished and kicks butt and saves Harry and Ron more times than anyone can count, so yes, Alice absolutely takes it as a compliment. And because Andrew knows this he has maybe called her Hermione a few more times after that first time because maybe it’s the only weirdly awkward way in which he feels comfortable complimenting her without sounding like he’s feeling a lot like Ron and much less like Harry in this friendship they have going on. (Yes, Andrew knows the story. No, he has never read the series, but yes, he has seen the movies).
So when Ewan says she looks very Hermione-esque in that soft tone because he’s so close to her lips, something in Andrew almost snaps. That’s his thing. His and Alice’s. And if someone’s going to turn that joking insult-that’s-not-really-an-insult into an actual compliment, complete with the leaning and brushing of lips against lips, it’s him, Andrew, and no one else!
So he interrupts them in a not so subtle way and curses the day Alice decided to do Pygmalion for this project.
Your head canon is approved and exactly right.
"There is one scene in the book where Gus goes to a gas station, and he tries to buy a pack of cigarettes because it’s the only way he can assert his own independence after becoming very sick. He [Ansel] did that scene so much justice, and he brought his all. It was midnight when we filmed it, and he just sat there and lost it for hours. I was just sort of in awe." - Shailene Woodley