That's definitely a typo because I've to read the sentence 3 times from the article still cannot make a sense until I saw the figure.
TL;DR, just buy one framework desktop and it's better than the Pi AI cluster of the OP in every single performance metrics including cost, performance, efficiency, headache, etc.
Oops, fixed the typo! Thanks.
And regarding efficiency, in CPU-bound tasks, the Pi cluster is slightly more efficient. (Even A76 cores on a 16nm node still do well there, depending on the code being run).
Slower. 4 times slower.