Do editors of other journals get asked to review papers? If editor of Journal A finds that the speciality of the editor of journal B is very close to the subject of a paper submitted to Journal A. Would the editor of journal A ask the editor of journal B to review the paper?
Probably not in their capacity as editor of journal B, but certainly probable in their capacity as known expert in the field (and if the fields are near, they'll probably have professional connections anyway).