Нет, в оригинале слова принадлежат Рону. Он или процитировал мать (если она это уже говорила), или прикинул, что она скажет.

Everyone filed out of the classroom except him and Ron, who was whacking his wand furiously on the desk.
“Stupid — useless — thing —”
“Write home for another one,” Harry suggested as the wand let off a volley of bangs like a firecracker.
“Oh, yeah, and get another Howler back,” said Ron, stuffing the now hissing wand into his bag. “‘It’s your own fault your wand got snapped — ’”
They went down to lunch, where Ron’s mood was not improved by Hermione’s showing them the handful of perfect coat buttons she had produced in Transfiguration.

Апд.: наверное, всё-таки Молли не знала про сломанную палочку, так что второе.