The VC10 was the first supercritical wing to enter service on an airliner, as far as I know. With that in mind, a strangely shaped diagram doesn't surprise me as they must have encountered a few new things along the way. We also know that the wing leading edge extension on the Super (and all but the BOAC Standards) wing was a compromise between redesigning a whole wing structure and an economical solution. So aerodynamically, the wing was not ideal. Later supercritical wings will have learned from this process, most likely sorted it out at an earlier stage and didn't have to deal with four hungry engines behind that wing center section either.
Just a bit of guesswork on my end, but it fits....