This is hugely damning against Manning and maybe Assange too. Even worse for Manning, in a chat with someone else, he admitted leaking the Apache attack video.
The data was in unallocated sectors. The logs had been deleted and someone had used security software to overwrite the unallocated sectors, but only overwrote them once. This is not nearly enough. 30-40 times is the standard for overwriting unused sectors, using varying patterns, so the data can not ever be recovered.
Manning also used his Mac Book password as the encryption key for the logs. This was beyond dumb. The precautions he took might have been worked against minor investigations but didn’t have a chance against military computer forensics experts.