You can just leave it behind without filling it out, but they're supposed to give one to every passenger. Or at least that what the flight attendant told me when handing out the form a couple days ago.
I don't take as strict of a stance in this situation. Yes, she's GE and perhaps should've know better. Sure, GE deserves greater scrutiny. And by the letter of the law, the customs agent is right.
But most of us wouldn't think of the apple given on the plane as something we're "importing". Easy to see how that slipped her mind. Pretty often I save airlines snacks for later, it'd be easy to forget this one was a fruit instead of biscoff cookies.