They don't need to be much more advanced than you. Also the article is talking about adults not children and also adults who have chosen the topic that they wish to learn so it is reasonable to expect that they will put some effort into the task. Very often it is much more effective to have another student explain something to another student than have the teacher try to explain it to a whole class or lecture theatre simply because the student realizes which bits are difficult because they have recently gone through the process of learning it. Anyway, this surely does not happen in a vacuum, both peers can surely use other resources in addition.
In a slightly different but related field in my career as an electronics engineer and software developer I have always found it valuable to have manuals written largely by users who have themselves recently learnt how to use my products rather than trying to write it all myself. Of course I give assistance and do a lot of proofreading but having the users teach each other is efficient because they can concentrate on the things that are actually important rather than the ones that were difficult, expensive, or intellectually interesting to create.
In a slightly different but related field in my career as an electronics engineer and software developer I have always found it valuable to have manuals written largely by users who have themselves recently learnt how to use my products rather than trying to write it all myself. Of course I give assistance and do a lot of proofreading but having the users teach each other is efficient because they can concentrate on the things that are actually important rather than the ones that were difficult, expensive, or intellectually interesting to create.