No, I don't think that's disturbing. That's the point of backups - even when something is permanently and completely erased in the production database, it's still in the backup. Eventually it will get rotated out as the backups expire.
Going back and purging things from the backups as part of the delete process would be overdoing it to a ridiculous degree.
Going back and purging things from the backups as part of the delete process would be overdoing it to a ridiculous degree.