Cheaper oil, indeed will not
“boost” the world economy. The fall in oil is, in part, a reflection of the economic slowdown. It is part of it. Separating out the components and considering them singly, cheaper oil, at best, keeps the economy from contracting as fast as it would were oil not cheaper.
The oil is cheaper in part because the dollar has gotten stronger, meaning is takes fewer of them to buy a barrel of crude. That and the greater supply of oil.
Now if you can explain to me how having people p!ss away less money filling their gas tanks every week is going to hurt the economy, instead of freeing up money they can spend on consumer goods, services, rent, etc... well, then I’d give this article some credence.