Most likely, the girl, not being smashed, woke up and screamed or punched him. Too bad she didnt have a knife under the pillow.
Agreed on all counts, although with the legal focus on 'knife crime' in the UK these days, the girl and / or her parents might have been afoul of the law merely for allowing an 'edged weapon' near her.
3,900 knives seized by police in stop and search operation News
She could say she took it out of the kitchen drawer while she was sleepwalking :-).