It means, for example, Google Messages uses E2EE backups. Google cannot read your E2EE messages by default, period. Not from your own backup, not from other peoples' backups. No backup loophole. Most other E2EE messaging apps also do not have a backup loophole like iMessage.

It's not hard to understand why Apple uploading every message to themselves to read by default is different from somebody intentionally taking a screenshot of their own phone.