Yes, there is some confusion there. The point they are making related to plants though is that, apparently, (some?) plants absorb diffuse light better than dire

Yes, there is some confusion there. The point they are making related to plants though is that, apparently, (some?) plants absorb diffuse light better than direct light. So, they claim that the photosynthesis efficiency would actually be enhanced by applying this extra layer to the glass, even though it still reduces the total amount of light going in (they haven't directly tested this, but they estimate the effect based on some other papers which quantified the efficiency of photosynthesis in diffuse vs direct light).