I do not know this word and it doesn't appear in the unabridged Random House Dictionary. It is a good one, though! From the context I would assume that it is being swept far out from one side to the other. Yes, "in a semicircle" is probably what is being meant, but "sidewide" is much more vivid, isn't it?
I do love new words. They only tend to work when the context is clear, however.
Bushwhacker, surely by now you understand that the writer of this "book" is not an English native, twists words so that they vaguely sound correct and that you must use your imagination and logic to understand.