If you open a document that has been shared with any kind of editing permission (even Comment-Only), you can see the profiles of everyone else who has also opened (or maybe even just seen) that doc.
Also it doesn’t matter if you revoke permissions. If anyone can copy the doc with a little trickery they can still see the other ‘peers’, only they’re Now Missing.
This is also true for the docs in the Template Gallery, where you can see the profiles of most Coda members. (Use the embed below to test it: just create a table with a ‘People’ column)