I was at the BAFTAs and the moment itself was odd, from Rebel's intro (which at the time actually sounded a little aggressive) to EW's reply. I hadn't noticed the 'bar one' until I saw the video but the response actually makes more sense now. And clearly set up.
From the crowd POV, "I'm here for all the witches" got an ok response (and a whoop) but I think if EW had said the entire thing out loud it wouldn't have gone down as well. It was quite a serious crowd - luvvies, yes - but I feel there's a reason EW didn't have the cojones to say the second part clearly.
She skipped over to Rebel afterwards and they hugged and giggled and were clearly very pleased with how it had gone. As I said, the lines were clearly staged. And a bit rubbish, considering.
My estimation of Emma Watson has sadly gone down since seeing that video. As someone posted earlier, despite their difference of opinion JKR has not slagged off the cast nor made disparaging remarks about them, unlike vice versa.
I feel the JKR hatred all stems somehow from young people fighting back against their mothers. She's the archetypal mother figure, isn't she? Beloved in a child's eyes, magical, pure - now they're fighting back, throwing punches against the thing they once loved most.