Comment by antonvs

Check out the paper - someone else linked it. It has several examples from Old English and other related languages which support its case. It seems pretty compelling to me.

The fact that earlier translators had to break up the original sentence and insert an exclamation point after "What" is already a bit suspect. Walkden's interpretation actually makes more sense, when you see examples like "Hwæt stendst þu her wælhreowa deor?", meaning "Why are you standing here, cruel beast?"

This may be a case where early translators over-indexed on e.g. Latin patterns and made a mistake which was then just accepted by subsequent translators.