Since reviews in double blind review are expected to deal with the paper as it is and not search for possible authors on line, I'd say that it is fine. Many papers have been seen by people other than the authors (collaboration circles, say) prior to submission.
If a reviewer somehow knows the author(s) they should inform the editor of the fact, but that is on them, not on the authors.
Double blind doesn't mean super secret. It is an attempt to get independent opinions on the value of a work, unaffected by external factors.
