I think it's stating that overqualified individuals are likely to get worse performance evaluations than if that same individual was in a job they were qualified for (e.g. they try harder when challenged and earn better ratings for themselves on a comparative basis), but are still more likely to get promoted than qualified/underqualified peers.

They did say they outperform persons better aligned to the job even though they are less happy. I'm guessing their review is worse relative to the same person in a job they aren't over qualified for, as opposed to comparing to another person in the same job who is not overqualified.

for sure. sometimes getting stuff done involves stepping on the wrong person's toes, even if it was completely unintended. we've all been there before! a strong boss is required to smooth things out in those situations