While the results are not unexpected i think the conclusion is questionable. Of course the recall for something you did not write will be lower, but to conclude from it, that this will impeded overall learning is in my opinion far fetched.

I think what we are seeing is that learning and education has not adapted to these new tools yet. Producing a string of words that counts as an essay has become easier. If this frees up a students time to do more sports or work on their science project that's a huge net positive even if for the essay it is net negative. The essay does not exist in a school vacuum.

The thing students might not understand is: their reduced recall will make them worse at the exam ... Well they will hopefully draw their own conclusion after first their failed exam.

I think the quantitative study is important but I think this qualitative interpretation is missing the point. Recall->Learning is a pretty terrible way to define learning. Reproducing is the lowest step on the ladder to mastery