What do they mean...
There are two parties involved in a peer review. One is the reviewer peer (of which there may be several), and the other is the reviewee peer. They approach the task in a spirit of shared respect and with a mutual desire for ever-increasing excellence, bringing to it a combination of knowledge, experience, open-mindedness and humility. They also bring to it a combination of paranoia, schadenfreude, insecurity, bitterness and malice sufficient to have kept Shakespeare in material for years. Or Webster: a stage littered with dead teachers by the end of Act One.
For reviewer peers, the review should be tremendous fun. For a few hours they can be omniscient. They can observe without comment, shake heads, make notes, be unsmiling and severe, or benevolent and encouraging. Most of all they can revel in the fact that some other poor sap has it worse than they do.
It can also be a nightmare, in which they discover that the reviewee peer is actually a damn sight better than they are. But at least only they will know, and they can compensate by being especially nasty in a helpful and constructive way.
For the reviewee peer, however, there is nowhere to hide, and the whole thing is a horror, in which every weakness shines forth and every strength is hiding behind the nearest bushel. And when the ghastly business is over, the reviewee peer has to say thank you. Especially for the advice on bushel management.