I am puzzled. They mention velcro doesn't work with rigid surfaces, but when they show a picture of what I assume is their solution, it seems to utilise ... "a flexible sheet material", i.e. a non-rigid surface.
Why are you puzzled? "Doesn't work with rigid surfaces" shows it working with a non rigid surface.
Of course what the article says is a true system didn't work with a rigid surface, but they came up with something close.
Perhaps the flexible sheet is just used so it can be peeled back to reveal the mechanics of the connecting bits--perhaps the flexibility is purely pedagogical.
