I thought the implication of the article, though, based on their research, was that this plant did not use all of the extra CO2 to grow, but used some of it to

I thought the implication of the article, though, based on their research, was that this plant did not use all of the extra CO2 to grow, but used some of it to produce more growth inhibitor which then cause crops to not grow. i.e. the experiment showed that the extra CO2 does not impact all plants in the same way, and does not necessarily impact plants in a way that is to the benefit of crops.