Hi Anton,
Octopart's algorithms constantly sift through our parts database, discovering entities with different uids which refer to the same part. We merge the entitites into one, and choose one of their uuids to serve as the "real" uid. The uid which was not chosen becomes a "redirected" uid. If you request a uid which has been redirected, you will be taken to the "real" uid. The redirected_uids field lets you confirm that indeed, we still recall storing the part you requested, but it has been merged into a different part.
Jimmy