I completely agree. Trying to get low level details out to the public while in the heat of the issue is a misstep; you can still be transparent while not risking over communication that could haunt you later.
While I think most of the HN audience understands that some days you have a bad day and that sometimes very small actions, like typing a single command at a prompt, can have dramatic consequences in technology, there are nonetheless less enlightened souls in hiring positions that simply might find fragments of this in a search on the name when that time comes.
Being too transparent could also encourage legal problems, too, if someone decides that they had a material loss over this, at least for the company. Terms of service or likelihood of a challenge prevailing doesn't necessarily matter: you can be sued for any reason and since there's no loser pay provision in any U.S. jurisdiction that I know of, even a win in court could be very costly. Being overly transparent in a case like this can bolster a claim of gross negligence (justified or not) and the law/courts/judges/juries cannot be relied upon to be consistently rational or properly informed.
Part of the problem is that this isn't actually a postmortem: they're basic live blogging/streaming in real time. What would be helpful for us (users) and them (GitLab) in terms of real-time transparency:
* Acknowledge there were problem during a maintenance and data may/may not have been lost.
* If some data is known to be safe: what data that is.
* What stage are we at. Still figuring it out? Waiting for backups to restore? Verification?
* Broad -estimated- time to recovery: make clear it's a guess. Even coarsely: days away, 10's of hours away, etc.
* When to expect the next public update on the issue.
None of this needs to be very detailed and likely shouldn't include actual technical detail. It just needs to be honest, forthright, and timely. That meets the transparency test while also protecting employees and the company.
Later, when there is time for thoughtful consideration, a technical postmortem at a good level of detail is completely appropriate.
[edit for clarity]