I assumed they had also shown some isolated improvement from a specific memory of failure alone, which was indeed surprising to me.

Some of the participants were asked to reflect on a number of their past successes or failures by completing the sentence: "In general, I'm successful (I fail) when...."

The other participants were focused instead on a single episode of success or failure, by completing the sentence: "I succeeded (failed) once when I had to...."

The results were remarkable. People who were asked to reflect on their many past successes or a specific failure scored roughly 10% better on tests of mathematical ability, as well as verbal, spatial, and abstract reasoning, than those who reflected on either many past failures or a single specific success.

So my report of the article was correct. So, if what you say is true, then the article misrepresented the study (which I also have not read).