I don't thing there's anything hidden in the screenshot.
If the filename is a GILD or A BitLocker ID, then it could be related to the dead man's password that Assange put out.
Best guess: Assange got a drive to Q's people with the Seth Rich leak info or similar.
Encrypted drive delivered. Once confirmed, password released by Assange on twitter. Over 3 weeks contents are looked over. Then, Q publishes the drive's ID to pre-prove future news.