Ofcourse they went public...
Maybe I'm too cynical here, I cannot rule this out, but in my opinion Gitlab didn't have a choice but to go public. For the simple reason of damage control.
Think about it: what do you think would have happened if they covered things up only to see the details leaked at a later time? Then it would become double trouble; not only would the community start criticizing them about their plain out ridiculous backup "strategy" as well as them trying to cover it all up. If they had gone this route and the details did eventually emerge then they could have definitely kissed their companies reputation goodbye, maybe even the entire company.
So I don't see any goodwill here, only simple damage control. BUT.. I may be a little overcritical.
Even so... Overlooking the fact that 100+Gb worth of data gets "archived" in files of a few kilobytes large has nothing to do with making a simple mistake, that is a plain out display of stupidity at its finest.